THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 
MRS.  PRUDENCE  W.  KOFOID 


A  TEXT-BOOK 

OF 

PHYSIOLOGY 
OTT 


A  TEXT-BOOK 


OF 


PHYSIOLOGY 


BY 


ISAAC  OTT,  A.M..  M.D. 

PROFESSOR  OF  PHYSIOLOGY  IN  THE  MEDICO-CHIKURGICAL  COLLEGE  OF  PHILADELPHIA 


WITH  137   ILLUSTRATIONS 


PHILADELPHIA 

F.  A.   DAVIS  COMPANY,  PUBLISHERS 
1904 


COPYRIGHT,  1904, 

BY 

F.  A.  DAVIS  COMPANY. 


[Registered  at  Stationers'  Hall,  London,  Eng.] 


Philadelphia.  Pa..  U.  S.  A. 

The  Medical  Bulletin  Printing-house. 

191 4-16  Cherry  Street. 


U   o°| 


PKEFACE. 


THIS  book  has  been  written  at  the  solicitation  of  students  who 
have  attended  my  lectures  for  the  past  eight  years.  The  aim  has  not 
been  to  write  a  treatise  on  the  subject,  but  rather  an  elementary  work 
containing  the  chief  facts  of  physiology  which  are  necessary  to  the 
student  who  wishes  to  apply  them  in  the  practice  of  his  profession. 
Physiology  is  the  basis  of  medicine,,  and  its  understanding  is  requisite 
to  the  study  of  pathology.  With  this  idea  in  mind,  small  space  has 
been  given  to  the  subject  of  electro-physiology.  The  technique  of  the 
laboratory  has  been  omitted  for  similar  reasons.  In  the  preparation 
of  this  book  it  was  found  impossible  to  give  due  credit  to  all  the 
sources  from  which  information  has  been  derived. 

The  illustrations  have  been  selected  from  various  authorities,  to 
whom  credit  has  been  given. 

ISAAC  OTT. 

APRIL,  1904. 


(61350145 


CONTENTS. 


THE  CELL 


CHAPTER  I.  PAGE 


CHAPTER  II. 

CHEMICAL  CONSTITUENTS  OF  THE  BODY  AND  FOODS  .....  24 

CHAPTER  III. 

DIGESTION  ...............................  42 

CHAPTER  IV. 

ABSORPTION   .............................  103 

CHAPTER  V. 

THE  BLOOD  ........................................  124 

CHAPTER  VI. 

THE  CIRCULATION  .......................................  163 

CHAPTER  VII. 

KESPIRATION  ............................................  237 

CHAPTER  VIII. 

SECRETION  ..............................................  277 

CHAPTER  IX. 

METABOLISM  .....................................  :  ......   328 

CHAPTER  X. 

ANIMAL  HEAT  ................................  ...........   338 

CHAPTER  XI. 
THE  MUSCLES  ..........................................  .  358 

CHAPTER  XII. 

VOICE  AND  SPEECH  .......................................   384 

CHAPTER  XIII. 

ELECTRO-PHYSIOLOGY   .......................  .............  394 

(vii) 


viii  CONTENTS. 

CHAPTER  XIV.  PAGE 

NERVOUS  SYSTEM 393 

CHAPTER  XV. 

TACTILE  SENSE 477 

CHAPTER  XVI. 

TASTE 488 

CHAPTER  XVII. 

SMELL 492 

CHAPTER  XVIII. 
HEARING 496 

CHAPTER  XIX. 
VISION 509 

CHAPTER  XX. 

CRANIAL  NERVES 530 

CHAPTER  XXI. 

EEPRODUCTION 547 

INDEX  .  557 


LIST  OF  ILLUSTEATIONS. 


FIG'  PAGE 

1.  Vegetable  Cell.     (DUVAL)    6 

2.  Cell  with  Reticulum  of  Protoplasm  Radially  Disposed.     From  Intes- 

tinal Epithelium  of  a  Worm.     (CARNOY)   8 

3.  Amoeba  Proteus.     (LEIDY)  14 

4.  Specimens  of  Milk,  viewed  through  the  Microscope.     (LANDOIS)   38 

5.  Dog's  Stomach.     (PAWLOW)    66 

6.  Liver  of  Man.     (DUVAL)    85 

7.  Taurin.      (DUVAL)    89 

8.  Glycocholic  Acid.     (DuvAL)    89 

9.  Crystals  of  Cholesterin.     (DuvAL) 91 

10.  Inhibitory  Apparatus  of  Ano-spinal  Center 102 

11.  Section  of  Dog's  Intestine  showing  the  Villi.     (CADIAT)   103 

12.  Diagram  of  the  Relation  of  the  Epithelium  to  the  Lacteal  in  a  Villus. 

(FUNKE)      .. . . 104 

13.  Lacteals  of  a  Dog  during  Digestion.     (COLIN)   105 

14.  Osmometer.     (COHEN)    110 

15.  Blood-corpuscles  of  Different  Animals.     (THANHOFFER)   128 

16.  Human  and  Amphibian  Blood-corpuscles.     (LANDOIS)   129 

17.  Hsemacytometer  of  Thoma-Zeiss.     (LAHOUSSE)   131 

18.  Red  Blood-corpuscles.      ( LANDOIS)    133 

19.  Leucocytes  of  Man,  showing  AnuEboid  Movement.     (LANDOIS)   135 

20.  Blood-plates  and  their  Derivatives.     (LANDOIS) 138 

21.  Blood-crystals   of   Man  and  Different  Animals.      (THANHOFFER  and 

FREY)    144 

22.  Teichmann's  Haemin-crystals.     (LAHOUSSE)    145 

23.  Sorby-Browning  Microspectroscope   147 

24.  Spectra    of   Oxyhaemoglobin,   Reduced   Haemoglobin,    and  CO   Haemo- 

globin.    (GAMGEE)  148 

25.  Von  Fleischl  Haemometer.     (LAHOUSSE)    150 

26.  Heart    of    the    Cow,   with   Left   Auricle   and   Ventricle   Laid    Open. 

(MULLER)     106 

27.  Diagram  of  Mammalian  Heart.     (BECLARD)    1<>7 

28.  Course  of  Muscular  Fibers  of  Heart.     (LANDOIS)   168 

29.  Course  of  the  Ventricular  Muscular  Fibers.     (LANDOIS)   169 

30.  Diagram  of  the  Circulation.     (DuvAL)    172 

31.  Sanderson  Cardiograph   .  176 

32.  Record  Obtained  with  the  Cardiograph  when  the  Button  is  Placed  at 

the  Apex-beat  of  the  Human  Heart.     (SANDERSON)   177 

33.  Heart  of  the  Frog.     (LivoN)   186 

34.  Schema  of  Ligatures  of  Stannius.     (HEDON)   188 

35.  Cardiac  Plexus  and  Stellate  Ganglion  of  the  Cat.     (LANIKMS)   190 

36.  Course  of  Vagus  Nerve  in  Frog.     ( STIRLING )   .101 

(ixj 


X  LIST  OF  ILLUSTRATIONS. 

FIG.  PAGE 

37.  Tracing  by  Lever  Attached  to  Frog's  Heart  on  Stimulation  of  the 

Pneumogastric  Nerve.     (FOSTER)    192 

38.  Manometer  Tracing  from  Rabbit,  on  Stimulation  of  the  Pneumogas- 

tric Nerve.     (FOSTER)  193 

39.  Scheme  of  the  Cardiac  Nerves  in  the  Rabbit.     (LANDOIS) 194 

40.  Blood-pressure  Tracing  Obtained  by  Stimulating  the  Depressor  Nerve 

in  a  Rabbit.     (FOSTER)    195 

41.  Weber's  Schema 201 

42.  Marey's  Intermittent  Afflux  Apparatus.     (LAHOUSSE) 204 

43.  Marey's  Sphygmograph.     ( YEO)   207 

44.  Tracings  Recorded  by  Marey's  Sphygmograph.     (YEO)  208 

45.  Frog's  Web,  Highly  Magnified.     (YEO,  after  Huxley]  210 

46.  Showing  the  Relative  Heights  of  Blood-pressure  in  Different  Blood- 

vessels.    (YEO)    213 

47.  Variations  in  Pressure.     (LANDOIS)    214 

48.  Manometer  of  Mercury  for  Measuring  and  Registering  Blood-pressure. 

(YEO)    216 

49.  Ludwig's  Kymograph.     ( YEO)   217 

50.  Blood-pressure  Curve  Recorded  by  the  Mercurial  Manometer.     (Yso).  218 

51.  Ludwig's  Stromuhr.      (LANDOIS)    223 

52.  Human  Respiratory  Apparatus.     (DuvAL)   241 

53.  Termination  of  a  Bronchus  in  an  Alveolus 244 

54.  Diagrammatic    Representation    of    the    Action    of    the    Diaphragm. 

(BECLARD)    247 

55.  The  Action  of  the  Ribs  in  Man  in  Inspiration.     (BECLARD)    248 

56.  Schema  of  Action  of  Intercostal  Muscles.     (LANDOIS)    249 

57.  Tracing  of  a  Respiratory  Movement.     (FOSTER)    251 

58.  Marey's  Tympanum  and  Lever.     (SANDERSON)   252 

59.  Scheme  of  Chief  Respirotory  Nerves.     (LAND;)IS,  after  RiitJicr-ord) 259 

60.  Arrest  of  Respiration  in  State  of  Expiration.     (HEDON) 260 

61.  Apparatus  for  Taking  Tracings  of  the  Movements  of  the  Column  of 

Air  in  Respiration.     (FOSTER)    262 

62.  Tracing  of  an  Experiment  with  Splenic  Extract  upon  a  Dog 284 

63.  I,  Dog.     Arrest  of  Peristalsis  by  30  Drops  of  Adrenalin.     II,  Dog. 

Arrest   of  Peristalsis  for  a  Minute  and  a  Half  by  20  Drops  of 
Adrenalin  Solution 286 

64.  Dog's  Mammary  Gland  in  First  Stage  of  Secretion.     (HEIDENHATN)  . .   291 

65.  Mammary  Gland  of  Dog,  Second  Stage  of  Secretion.     (HEIDENIIAIN)..   292 

66.  Section  of  Sweat-glands  of  Cat.     (Colored) 295 

67.  Relations  of  the  Kidney.     (After  SAPPEY)   300 

68.  Section  of  Kidney.     (LANDOIS)   302 

69.  Diagram  of  the  Course  of  Two  Uriniferous  Tubules.     (LANDOIS) 303 

70.  Bowman's  Capsule  and  Glomerulus,  "Rodded  Cells"  from  a  Convo- 

luted Tubule,  Cells  Lining  Henle's  Looped  Tubule,  Cells  of  a  Col- 
lecting Tube,  and  Section  of  an  Excretory  Tube.      (LANDOIS)    304 

71.  Blood-vessels  and  Uriniferous  Tubules  of  the  Kidney   (Semidiagrarn- 

matic).     (LANDOIS) 306 

72.  Longitudinal  Section  of  a  Malpighian  Pyramid.     (LANDOIS)     307 


LIST  OF  ILLUSTRATIONS.  x[ 

FIG.  PAGB 

73.  Uric- Acid  Crystals  with  Amorphous  Urates.     (PURDY,  after   Peyer.) 

( Colored ) 312 

74.  Leucin  in  Balls ;    Tyrosin  in  Sheaves.     (PEYER)   315 

75.  Crystals  of  Ammonio-magnesium  Phosphate.     (After  ULTZMANN)   . .  320 

76.  Crystals  of  Phenylglucosazone.     ( PURDY,  after  v.  Jaksch.)    (Colored)  32.'J 

77.  Human  Calorimeter    345 

78.  Bilateral   Puncture  of  the  Tuber   Cinereum   of   Rabbit  Through  Roof 

of  Mouth    350 

79.  Cortex  of  Cat's  Brain   351 

80.  Lesions  of  Cortex  in  Man  Causing  Elevations  of  Temperature 352 

81.  Curves  of  Temperature  and  Respiration  when  Cortex  is  Removed  and 

the  Animal  is  Artificially  Heated 353 

82.  Curve  of  Temperature  and  Respiration  when   the  Tuber  Cinereum  is 

Destroyed  and  the  Animal  is  Artificially  Heated 354 

83.  Heat  Production  and  Heat  Dissipation  in  Man  during  a  Paroxysm  of 

Malarial  Fever — a  Great  Increase  of  Heat  Production 355 

84.  Histology  of  Muscular  Tissue.     (ELLENBERGER)   361 

85.  Unstriped  Muscular  Tissue.    (ELLENBERGER)    368 

86.  The  Pendulum  Myograph.     (FOSTER)    374 

87.  Muscle-curve  Obtained  by  Means  of  Pendulum  Myograph.    (FOSTER)  .   370 

88.  Arrangement  of  Apparatus  in  Conducting  Experiments  on  Nerve  and 

Muscle.     (STIRLING)    377 

89.  Apparatus  for  Measuring  the  Velocity  of  the  Wave  of  Muscular  Con- 

tractions.    (MAREY)    378 

90.  Tracing  of  a  Double  Muscle-curve.     (FOSTER)   379 

91.  Tetanus  Produced  with  the  Ordinary  Magnetic    Interrupter    of    an 

Induction  Machine.     (FOSTER)   380 

92.  Muscle  Thrown  into  Tetanus,  when  the  Primary  Current  of  an  Induc- 

tion Machine  is  Repeatedly  Broken  at  the  Rate  of  Sixteen  Times 
per  Second.     (FOSTER)    381 

93.  The  Larynx  as  Seen  with  the  Laryngoscope.    (LANDOIS)    385 

94.  Action  of  the  Muscles  of  the  Larynx.     (BEAUNis)   386 

95.  Schematic  Horizontal  Section  of  Larynx.     (LANDOIS)  387 

96.  Schematic  Closure  of  the  Glottis  by  the  Thyro-arytenoid  Muscles. 

(LANDOIS)     388 

97.  Position  of  Vocal  Cords  on  Uttering  a  High  Note.     (LANDOIS)   390 

98.  The  Nerve-muscle  Preparation.     (STIRLING)    395 

99.  The  Structure  of  Nervous  Tissue.     (LANDOIS)     3!M» 

100.  Transverse  Section  of  the  Spinal  Cord 416 

101.  Medulla  Oblongata,  Pons,  Cerebellum,  and  Pes  Pedunculi.    Anterior 

View,  to  Demonstrate  Exits  of  Cranial  Nerves.     (EDINGER)   421 

102.  The  Three  Pairs  of  Cerebellar  Peduncles.     (After  HIRSCHFELD  and 

LEVEILLE) 423 

103.  Cross-section    of    the   Oblongata    through    the    Decussation    of    the 

Pyramids.     (After  HENLE)    427 

104.  The  Base  of  the  Brain.    The  Left  Lobus  Temporalis  is  in  Part  Repre- 

sented as  Transparent  in  order  that  the  Entire  Course  of  the 
Optic  Tract  might  be  Seen.     (EDINGER)   429 


xii  LIST  OF  ILLUSTRATIONS. 

FIG.  PAGE 

105.  The  Fillet,  Ending  Chiefly  in  the  Ventral  Nucleus  of  the  Optic  Thal- 

amus   and   then   United   by   New   Neuraxons    (Upper   Fillet)    to 
Parietal  Cortex 434 

106.  Section  through  the  Cerebral  Cortex  of  a  Mammal.     (EDINGER  and 

CAJAL)    437 

107.  Curves  Illustrating  the  Measurement  of  the  Velocity  of  a  Nervous 

Impulse  (Diagrammatic) .     (FOSTER)   446 

108.  Scheme  of  Electro-tonic  Excitability   447 

109.  Diagram  of  the  Roots  of  a  Spinal  Nerve  Showing  Effect  of  Section. 

(LANDOIS)    454 

110.  Horizontal  Section  through  the  Cerebellum.     (After  B.  STILLING)    . .   463 

111.  Effects  of  Removal  of  Cerebellum.     (DALTON)  466 

112.  Left  Cerebral  Hemisphere  in  Man,  Showing  Areas  of  Localization  . .  .   470 

113.  Left  Cerebral  Hemisphere  in  Man,  Showing  Areas  of  Localization  ...   471 

114.  Effects  of  Ablation  of  Cerebrum.     (DALTON)   473 

115.  Structure  of  the  Taste-organs.     (LANDOIS)   490 

116.  Diagram  of  the  External  Surface  of  the  Left  Tympanic  Membrane. 

(HENSEN)     497 

117.  Tympanic  Membrane  and  Auditory  Ossicles,  seen  from  the  Tympanic 

Cavity.     (LANDOIS)   498 

118.  Left  Tympanum  and  Auditory  Ossicles.      (LANDOIS)   499 

119.  Scheme  of  the  Organ  of  Hearing.     (LANDOIS)    500 

120.  Scheme  of  the  Labyrinth  and  Terminations  of  the  Auditory  Nerve. 

(LANDOIS)    501 

121.  Section  through  the  Uncoiled  Cochlea  (I)  and  through  the  Terminal 

Nerve  Apparatus  of  the  Cochlea  (II).     (MuNK,  after  Hensen}   .  . .   502 

122.  Section  of  the  Ductue  Cochlearis  and  the  Organ  of  Corti.     (After 

(LANDOIS) 503 

123.  I.  The  Mechanics  of   the  Auditory  Ossicles.      (After  HELMHOLTZ.) 

II.  Section  of  the  Middle  Ear.     (MUNK,  after  Hensen)  505 

124.  Diagram  of  a  Horizontal  Section  through  the  Human  Eye.     (¥EO)  . .   510 

125.  Vertical  Section  of  Human  Retina.     (LANDOIS)   514 

126.  Diagram  Illustrating  Spherical  Aberrations.     (GANOT)    519 

127.  Scheme  of  Accommodation  for  Near  and  Distant  Objects.     (LANDOIS, 

after  Helmholtz)   520 

128.  Myopic  Eye.     (LANDOIS)    521 

129.  Hypermetropic  Eye.     (LANDOIS)    » 521 

130.  Different  Kinds  of  Lenses.     (GANOT)   522 

131.  Diagram  Showing  Refraction  by  a  Double  Convex  Lens.     (GANOT)   . .   523 

132.  Diagram  Illustrating  the   Decomposition   of   White  Light  into  the 

Seven    Colors    of    the    Spectrum    in    Passing    Through    a    Prism. 
(BECLARD)    524 

133.  Diagram  Illustrating  Irradiation.     (STIRLING) 526 

134.  Diagram  Illustrating  Binocular  Vision.     (BECLARD)    528 

135.  Position   of    the  Nuclei  of    the   Cranial    Nerves.     (After   EDING  R. ) 

(Colored) 533 

136.  Human  Spermatozoa.     (MANTON)    549 

137.  Ovum  of  Rabbit.     (MANTON)    550 


CHAPTER  I. 

THE  CELL. 

OBSERVATION"  and  experience  tell  us  that  all  tangible  or  material 
things  about  us  are  either  dead  or  alive ;  that  is,  matter  is  either  life- 
less or  living. 

The  conception  of  life  in  its  simplicity  is  limited  to  a  few  ele- 
mentary phenomena,  as  nutrition,  evolution,  reproduction,  sensibility, 
and  motion.  These  properties  taken  together  distinguish  the  living 
from  every  form  of  lifeless  substance.  Combinations  of  these  simple, 
elementary  phenomena  give  us  every  complex  occupation  of  our  present 
life.  If  the  study  of  life  is  the  study  of  these  elementary  phenomena, 
it  is  necessary  that  our  working  force  be  brought  to  their  seat  and 
home — the  cell. 

Everywhere  there  is  a  sharp  line  or  division  between  living  and 
lifeless  matters,  although  the  two  are  frequently  so  closely  allied  that 
first  observations  seem  to  show  no  distinctions.  This  is  particularly 
true  of  those  things  that  are  not  seen  with  the  naked  eye — micro- 
scopical things.  When  one's  attention  is  brought  to  such  materials 
as  quartz,  iron,  the  earthworm,  or  the  dog,  the  distinction  is  very 
evident.  On  the  other  hand,  long  and  tireless  observation  and  investi- 
gation are  required  to  determine  whether  some  of  the  bodies  found  in 
water  are  dead  or  alive.  And  although  so  closely  associated,  scientists 
have  found  that  living  substance  never  comes  of  its  own  accord  from 
the  lifeless,  but  only  through  the  influence  of  some  other  living  matter. 
For  example,  no  vegetation  springs  up  from  the  soil  until  the  seed 
(a  form  of  dormant  life)  becomes  buried  in  it;  no  colony  appears  for 
the  bacteriologist  on  the  sterilized  medium  until  the  surface  is  impreg- 
nated with  the  germ. 

Although  the  sharp  distinction  exists,  nevertheless  the  two  mate- 
rials are  very  closely  associated,  as  is  shown  by  a  little  observation. 
Plants  and  animals  are  kept  alive  and  nourished  by  the  food  they  con- 
sume, which  consists,  in  the  main,  of  lifeless  matter.  While  in  the 
body  it  seems  to  be  transformed,  as  it  were,  to  a  living  state,  as  it 
forms  part  of  the  body.  After  it  has  served  the  needs  of  the  economy 
of  the  plant  or  animal  it  dies,  and  is  gotten  rid  of  as  waste-matter. 

(1) 


2  PHYSIOLOGY. 

A  living  plant  or  animal  is  like  a  fountain  into  which  and  out 
of  which  material  is  constantly  passing,  but  the  fountain  maintains 
its  form  and  general  appearance.  Huxley's  simile  of  a  whirlpool  in 
a  stream  is  very  striking.  The  pool  remains  the  same  in  the  stream, 
but  water  enters  it,  being  part  of  it  as  it  is  being  whirled  around,  and 
then  as  it  passes  out  gives  place  for  other  water.  The  pool  retains 
its  identity  all  the  while  that  its  elements  are  being  changed. 

The  contrast  between  living  matter  and  lifeless  matter  forms  the 
basis  of  the  separation  of  the  natural  sciences  into  two  divisions :  the 
biological  and  physical  sciences,  biology  dealing  with  living  and 
physics  with  lifeless  matter. 

Biology  is  the  science  that  treats  of  living  things,  whether  animal 
or  vegetable,  normal  or  abnormal.  It  deals  with  the  forms,  structures, 
and  origin,  together  with  the  functions  and  activities  of  the  whole 
animal  or  plant  or  its  various  parts.  In  fact,  its  scope  is  so  wide  and 
comprehensive  that  it  becomes  necessary  to  divide  it  into  two  branches : 
morphology  and  physiology. 

Morphology  is  that  part  of  the  science  that  deals  with  the  form 
and  structure  of  living  things,  together  with  their  arrangements. 

Physiology  is  the  science  that  treats  of  the  functions  or  work 
of  the  various  parts  of  the  living  organism  and  what  each  one  does 
toward  the  economy  of  the  whole.  For  instance,  the  study  of  the 
form,  growth,  and  development  of  the  different  parts  of  the  brain, 
beginning  with  the  lamper-eel,  then  the  higher  fishes,  birds,  and  mam- 
mals, belongs  to  the  science  of  morphology.  By  the  comparisons  we 
see  that  in  the  lamper  there  is  merely  the  semblance  of  a  brain  in  its 
crudest  form,  showing  no  development  as  compared  with  the  brain  of 
the  higher  fishes  and  birds.  In  them  we  notice  a  stronger  develop- 
ment in  one  department — the  optic  lobes.  The  cerebral  portion  is 
very  weak.  In  mammals  the  reverse  is  true,  and  reaches  its  most 
striking  size  in  man,  in  whom  the  cerebral  portions  are  extremely  large 
and  well  developed  and  the  optic  lobes  relatively  very  small. 

The  study  of  the  functions,  for  instance,  of  the  heart  and  kidneys 
belongs  to  the  science  of  physiology;  how  the  heart  by  its  alternate 
contractions  and  relaxations  forces  the  blood  through  the  circulatory 
system  to  the  peripheral  parts  of  the  body  for  its  sustenance  and  nutri- 
tion and  to  the  lungs  for  its  purification  by  the  elimination  of  the 
carbonic  acid  and  the  absorption  of  the  oxygen;  how  the  kidneys  by 
means  of  their  mass  of  tubes  and  cells  take  from  the  blood  those  parts 
that  are  no  longer  of  any  use  and  fit  only  to  be  expelled  from  the  body. 
When  physiology  is  applied  to  man  it  is  called  human  physiology,  for 


THE  CELL.  3 

the  understanding  of  the  functions  of  ourselves  is  the  great  and  ulti- 
mate end  and  aim  of  all  physiological  studies.  Morphology  and 
physiology  are  treated  as  though  they  were  absolutely  distinct  sciences, 
yet  they  are  so  closely  related  that  the  division  is  made  only  for  con- 
venience. 

Morphology  includes  in  its  category  such  subdivisions  as  anatomy, 
histology,  and  embryology. 

Anatomy  is  the  science  that  treats  of  the  situation,  form,  and 
structure  of  the  various  parts  of  the  organism.  Anatomy  from  its 
root  keeps  in  mind  the  idea  of  cutting  or  dissection,  and  as  commonly 
used  at  the  present  time  deals  with  the  grosser  work  done  upon  the 
more  common  and  apparent  structures  of  the  body  with  scalpel  and 
forceps.  When  we  describe  in  all  their  detail  the  different  organs  of 
the  body  and  the  position  of  the  organs  to  one  another  we  call  it 
descriptive  anatomy. 

Contrasted  with  anatomy  is  histology,  sometimes  called  micro- 
scopical anatomy.  Histology  is  the  science  that  deals  with  the  inti- 
mate structure  of  the  various  tissues  of  an  organism.  It  takes  up  the 
work  where  anatomy  stops,  as  it  brings  to  its  aid  the  microscope  and 
so  can  delve  down  deeper  and  deeper  until  it  gives  us  knowledge  of  the 
component  parts  of  the  various  organs.  Histology  is  a  tissue-study. 
Its  division  from  anatomy  is  only  one  for  convenience,  and  is  not 
absolute. 

Embryology  is  the  science  of  the  development  of  the  adult  from 
the  ovum  or  germ.  It  gives  a  history  from  the  moment  of  impregna- 
tion of  the  ovum,  through  the  various  stages  of  development  until  the 
adult  is  reached.  Its  field  is  more  closely  associated  with  morphology 
than  physiology. 

Living  things  are  usually  found  in  separate  masses  which  have 
peculiarities  and  structures  of  their  own  which  give  to  them  the  name 
"organisms."  This  is  true  equally  of  the  large  masses,  as  the  elephant 
or  whale,  as  of  the  small  bodies  found  in  water  or  the  bacteria  of  dis- 
ease. The  structures  of  the  latter  have  as  yet  not  all  been  discovered 
and  dissected,  as  it  were,  since  the  microscope  is  not  powerful  enough 
and  our  supply  of  reagents  not  adequate  enough  to  lay  bare  all  of  their 
properties  and  forms. 

When  we  examine  some  of  the  contrivances  found  in  the  mechan- 
ical world,  such  as  a  watch  or  machine,  they  at  first  sight  appear  to  us, 
as  regards  their  identity,  single  individual  units;  that  is,  one  watch 
or  one  machine,  each  capable  of  doing  its  own  peculiar  work.  Upon 
closer  investigation  we  perceive  that  each  is  composed  of  a  variety  of 


4  PHYSIOLOGY. 

individual  parts,  each  of  which  has  its  own  peculiar  share  of  the  work 
to  do  and  bears  an  essential  relation  to  the  working  of  the  whole.  In 
the  watch,  the  springs,  pinions,  levers,  and  numerous  little  wheels  all 
bear  certain  relations  to  one  another  and  assist  in  the  running  of  the 
watch. 

Similarly  we  find  that  it  is  characteristic  of  any  living  body  or 
organism — say,  a  dog  or  a  rose — that  it  should  be  made  up  of  a  num- 
ber of  different  and  distinct  parts  which  are  so  constructed  that  they 
may  assist  in  the  life  of  the  whole  organism.  The  animal  has  a  head, 
trunk,  limbs,  eyes,  ears,  etc.,  externally;  heart,  lungs,  liver,  stomach, 
intestines,  brain,  etc.,  internally.  To  these  parts  the  name  organs 
has  been  applied.  Thus,  the  organism  is  composed  of  distinct  parts 
called  organs.  The  division  of  the  body  into  organs  is  purely  arti- 
ficial. 

An  organ  is  a  particular  part  of  the  organism  that  has  a  certain 
specified  work  to  do.  For  example,  the  liver  is  a  certain  structure 
found  in  a  particular  situation  in  the  animal  and  which  has  assigned 
as  its  share  of  the  work  of  the  general  economy  the  manufacture  of 
the  bile  to  aid  digestion.  So,  also,  the  eye  and  the  stomach  are  organs. 
They  are  particular  parts  of  the  organism  concerned  in  particular 
work ;  the  eye  in  sight,  or  vision ;  the  stomach  in  digestion. 

The  work  which  any  organ  does  is  called  its  function.  Since  the 
appearance  and  structure  of  the  various  organs  of  a  living  body  are  so 
varied,  we  do  not  expect,  therefore,  that  their  functions  are  any  more 
the  same  than  the  functions  of  the  watch  and  locomotive.  Thus,  the 
function  of  the  heart  is  to  pump  the  blood  to  all  parts  of  the  body,  of 
the  blood  itself  to  carry  nutritious  food  to  all  parts  and  at  the  same 
time  carry  away  certain  waste-products,  of  the  kidneys  to  excrete 
waste-matters  from  the  blood,  the  brain  to  have  a  general  oversight  and 
govern  the  functions  of  the  whole  organism,  etc. 

Anatomy  is  the  forerunner  of  physiology  and  must  pave  the  way 
for  it.  For  how  are  we  to  study  the  functions  of  the  various  organs 
and  their  relations  to  one  another  unless  we  are  acquainted  with  the 
structure,  form,  and  position  in  the  body  of  the  various  organs  ?  Even 
while  studying  physiology  anatomy  must  run  hand  in  hand  with  it, 
particularly  that  modified  form  of  anatomy — histology,  or  micro- 
scopical anatomy — which  deals  with  the  minute  structures  and  their 
components — the  cells. 

We  have  learned  that  the  various  portions  of  the  living  body  are 
called  organs.  As  we  know,  each  organ  has  its  own  particular  work  to 
do.  By  careful  dissection,  we  find  that  an  organ — :a  human  arm,  for 


THE  CELL.  5 

instance — is  made  up  of  a  variety  of  substances  called  tissues.  There 
are  bone-tissues,  cartilaginous  tissues,  muscle-tissues,  nerve-tissues,  etc., 
all  different  in  structure,  yet  all  bundled  up  in  the  member  called  the 
arm  and  essential  to  it  to  perform  its  various  functions.  The  brain 
is  composed  of  two  distinct  parts — the  gray  and  white  tissues.  So, 
in  like  manner,  any  of  the  organs  of  the  body  may  be  resolved  into 
various  parts  known  as  tissues. 

Thus  far  anatomy  has  aided  us  in  our  analysis  of  the  various 
parts  of  the  body,  for  it  has  to  deal  with  only  the  grosser  and  more 
coarse  and  obvious  forms  of  the  body.  So  for  a  long  time  physiology 
was  the  study  of  those  large  and  more  evident  organs.  Physiology 
could  not  go  further  until  it  had  more  exact  and  intimate  knowledge 
of  the  organs.  How  can  we  gain  correct  knowledge  of  the  working  of 
any  machine  unless  we  first  know  and  understand  the  construction 
of  the  parts  of  the  machine  ? 

Chemistry  and  physics  teach  us  that  matter  is  made  up  of  simple 
forms,  called  elements  and  molecules,  respectively.  It  is  assumed  that 
the  units,  ultimately,  of  these  elements  and  molecules  are  definite, 
though  exceedingly  small,  material  particles.  These  particles  are 
called  atoms — the  word  meaning  that  the  particles  are  unable  to 
be  divided  without  losing  their  identity.  The  atom  of  the  chemist 
and  the  cell  of  the  physiologist  are  the  final  divisions  of  matter.  In 
the  physical  world  it  was  found  that  all  phenomena  were  due  to  the 
movements  of  these  small  particles — the  atoms. 

The  fact  that  animals  and  plants,  although  very  different  ex- 
ternally, are  made  up  of  the  same  anatomical  units  was  not  brought 
to  light  until  the  invention  of  the  microscope.  These  structural  units 
were  called  cells.  The  theory  that  organisms  were  made  up  of  cells 
was  suggested  by  the  study  of  plant-structure.  At  the  end  of  the 
seventeenth  century  scientists,  by  means  of  their  low-power  micro- 
scopes, discovered  in  plants  small,  roomlike  spaces,  provided  with 
firm  walls  and  filled  with  fluid.  Because  of  their  similarity  to  the 
large  cells  of  the  honeycomb  these  small  structures  received  the  name 
of  cells.  To  their  minds,  however,  the  principal  feature  seemed  to 
be  the  firm  walls.  By  study  they  found  that  the  cell  absorbed  nutrient 
material,  assimilated  it,  and  produced  new  material.  Although  plants 
were  composed  of  a  mass  of  cells  or  even  a  single  cell,  it  was  found  that 
each  cell  was  an  isolated  whole;  that  it  nourished  itself  and  built 
itself  up.  The  cell-theory  was  also  applied  to  animal  tissues.  By  its 
use  it  was  found  that  many  of  the  tissues  were  formed  also  of  cells  and 
that  these  cells  appeared  to  be  of  similar  construction  to  those  in  plant 


6  PHYSIOLOGY. 

life.  Thus  we  find  that  every  tissue  is  composed  of  minute  parts 
known  as  cells  and  which  in  a  particular  tissue  are  nearly  or  quite 
similar.  For  instance,  in  examining  a  muscular  fiber  we  find  that  it  is 
composed  of  very  small,  ribbonlike  units  called  .muscle-cells.  Although 
differing  somewhat  in  size  and  development,  yet  they  are  otherwise 
similar.  That  is,  muscular  tissue  is  composed  of  muscular  units,  or 
cells.  Cartilage  is  composed  of  oystershell-shaped  cells;  mucous- 
membrane  cells  are  gobletlike,  and  secrete,  or  give  off,  mucus.  Even 
though  these  cells  are  self-supporting  and  grow  and  form  other  cells, 
in  the  higher  animals  the}''  are  grouped  and  held  together  by  means  of 
a  kind  of  cement,  spoken  of  as  "intercellular  material." 

Hence  a  tissue  may  be  defined  as  a  group  of  similar  cells  having 
a  similar  function.     Tissues  are  different  only  because  they  are  com- 


Fig.  1.— Vegetable  Cell.     (DuvAL.) 
up,  Cell-wall  of  cellulose,    n,  Nucleus,     ch,  Chlorophyll  bodies. 

posed  of  different  kinds  of  cells  having  functions  peculiar  to  them- 
selves. -  An  aggregation  of  cartilage-  and  muscle-  cells  give  us,  respec- 
tively, cartilage-  and  muscle-  tissues. 

As  the  result  of  this  knowledge,  physiology  is  beginning  to  develop 
from  a  science  of  the  organ  and  its  functions  to  that  of  the  cell  and  its 
functions.  But  this  is  only  natural  as  a  form  of  development,  since 
we  first  consider  the  greater  and  more  active  functions  of  the  organs 
and  then  delve  down  deeper  and  deeper  until  we  reach  the  functions 
of  the  cell. 

Cells  are  characterized  by  the  presence  of  the  elementary  functions 
or  phenomena  of  nutrition,  growth,  reproduction,  etc.  If  physiology 
has  to  deal  with  them,  it  can  do  it  most  successfully  by  studying  them 
in  their  seat — the  cell. 


THE  CELL.  7 

The  vegetable  cell  is  known  from  the  animal  cell  by  the  presenc< 
of  cellulose. 

The  cell  of  the  vegetable  kingdom  takes  in  oxygen  and  gives  off 
carbonic  acid,  as  we  do,  but  the  action  of  the  sun's  rays  upon  the 
chlorophyll  causes  it  to  break  up  the  carbon,  fix  it  in  the  tissues,  and 
give  off  oxygen.  This  fixation  of  carbon  overshadows  in  daylight  the 
ordinary  respiration  of  the  plant,  which  goes  on  both  by  day  and  by 
night.  Yeast-cells  break  up  sugar  into  alcohol  and  carbonic  acid. 
Besides  this  action  they  have  in  them  a  ferment,  invertin,  which 
changes  cane-sugar  into  invert-sugar,  which  is  a  mixture  of  dextrose 
and  laevulose. 

CELLS. 

We  have  learned  that  the  higher  forms  of  life,  whether  plants  or 
animals,  may  be  resolved  into  a  vast  number  of  very  small,  structural 
units,  called  cells.  The  skin,  muscles,  bone,  brain,  etc.,  appear  to 
the  naked  eye  to  be  composed  of  one  kind  of  substance  respectively. 
The  microscope,  however,  has  told  us  that  each  tissue  is  composed  of 
colonies  of  units,  held  together  by  intercellular  cement,  and  that  the 
units  or  cells  of  a  particular  tissue  are  similar  in  structure  and  func- 
tions. For  example,  upon  examination  we  find  that  muscular  tissue 
is  made  up  of  ribbonlike  fibers,  similar  in  appearance  and  structure 
and  all  engaged  in  the  same  function— contraction.  Thus,  the  cell 
is  not  only  the  unit  of  structure,  but  also  of  function,  diseased  or 
normal. 

Animal  cells  are  of  various  sizes.  Although  differing  very  much 
in  shape  and  appearance  in  various  parts  of  the  body,  nevertheless 
every  cell  consists  of  the  following  parts :  (1)  protoplasm,  (2)  nucleus, 
(3)  centrosomes,  and  (4)  various  matters  commonly  called  "special 
cell-constituents." 

Max  Schultze's  definition  of  a  cell,  enlarged  by  later  research,  is : 
tfA  mass  of  protoplasm  containing  a  nucleus." 

The  term  cell  as  employed  to-day  is  a  misnomer,  but  from  its 
constant  use  since  the  seventeenth  century  it  has  gained  such  a  hold 
upon  the  minds  of  those  engaged  in  the  study  of  science  that  the 
attempt  to  supersede  it  with  a  more  appropriate  term  has  been  unsuc- 
cessful. However,  the  idea  that  it  originally  conveyed  has  been  modi- 
fied somewhat.  The  term  originated  among  the  botanists  of  the 
seventeenth  and  eighteenth  centuries,  and  was  applied  to  chamberlike 
elements,  separated  from  one  another  and  containing  a  fluid.  The 
characteristic  and  most  important  feature  of  them  was  the  wall  or 


8 


PHYSIOLOGY. 


membrane,  and  in  it  were  supposed  to  lie  active  properties  of  the  cell. 
The  liquid,  originally  called  plant-slime,  was  named  protoplasm  by 
von  Mohl,  and  was  thought  to  be  a  waste-product. 

That  the  wall  or  membrane  was  not  of  vital  importance  was 
clearly  demonstrated  by  later  researches.  The  study  of  the  amoeba 
and  white  blood-corpuscle,,  one-celled  organisms,  was  the  chief  means. 
These  organisms  are  capable  of  extending  their  bodies  into  processes 
— fine  threads  and  networks — as  they  move  about  from  place  to  place, 
taking  up  and  giving  off  matter  as  they  go.  They  possess  all  the 
elementary  vital  functions,  and  yet  at  no  time  do  they  possess  a  cell- 
membrane,  showing  that  the  protoplasm,  not  the  membrane,  was  the 


Cell-membrane,  jg 


Reliculnm  of  cell 


Membrane  of  nucleus 


Nuclear    achromatic 
substance 


Nuclear  chromatic 
substance 


Fig.  2. — Cell  with  Reticulum  of  Protoplasm  Radially  Disposed.    From 
Intestinal  Epithelium  of  a  Worm.     (CAKNOY.) 

seat  of  the  functions.  An  immense  number  of  other  unicellular 
organisms  was  examined,  together  with  the  development  of  other 
plants  and  animals,  and  many  cells  devoid  of  a  membrane  were  found. 

PROTOPLASM. 

The  protoplasm  of  unicellular  organisms  appears  as  a  viscid  sub- 
stance, which  is  almost  always  colorless  and  will  not  mix  readily  with 
water.  The  name  of  protoplasm  is  constantly  in  the  mouths  of  the 
physiologists,  and  it  is  difficult  to  give  a  rigid  definition  of  the  word, 
as  it  is  used  in  so  many  different  senses.  Hence,  we  commonly 
describe  protoplasm  as  a  living  substance  surrounding  a  nucleus,  which 
substance  may  or  may  not  be  limited  by  a  cell-wall. 


THE  CELL.  9 

Its  refractive  power  is  greater  than  that  of  water  and  in  it  as  a 
medium  very  delicate  threading  of  protoplasm  may  be  distinguished. 
It  was  formerly  supposed  to  be  composed  of  a  homogeneous  material, 
destitute  of  any  structure  and  containing  a  number  of  minute  granules 
of  a  solid  nature. 

Under  the  high  powers  of  the  microscope,  when  properly  stained 
with  reagents,  it  has  been  found  that  the  protoplasm  consists  of  two 
parts :  (1)  a  fine  network  of  fibers,  like  a  sponge,  called  the  reticulum, 
or  spongioplasm;  and  (2)  the  more  fluid  portion  in  the  meshes,  called 
the  enchylema,  or  hyaloplasm.  However,  it  must  be  mentioned  that 
the  views  concerning  the  structure  of  protoplasm  are  divided,  several 
theories  being  offered.  According  to  the  first  idea,  the  protoplasm 
forms  the  network,  the  nodal  points  of  which  appear  as  individual 
granules.  It  is  very  probable  that  many  of  the  larger  and  more 
obvious  of  them  are  inert  bodies,  such  as  glycogen,  mucin,  fat-globules, 
albuminous  substances,  etc.,  suspended  in  the  network.  The  glycogen 
granules  are  found  in  the  liver-cells,  the  fat-globules  in  the  cells  of 
the  lacteal  glands,  and  the  pigment-granules  in  the  skin-cells  of  many 
colored  animals.  Sometimes  in  unicellular  animals  are  found  cal- 
careous matters,  although  those  most  uniformly  found  are  of  the  same 
general  nature  as  the  protoplasm.  All  these  particles  or  granules  are 
termed  microsomes.  Besides,  there  are  occasionally  found  indigestible 
bodies,  such  as  grains  of  sand,  indigestible  residue  of  foodstuffs  and 
excretory  substances,  waiting  to  be  expelled  from  the  body. 

Other  substances  found  within  the  protoplasm  and  supposed  to 
be  of  great  importance  to  cell-life  are  drops  of  liquid — vacuoles,  as 
they  are  commonly  called. 

Specific  Gravity  of  Living  Protoplasm. 

Living  protoplasm  has  the  physical  property  of  having  a  greater 
specific  gravity  than  water.  When  cells  of  the  most  varied  kinds  are 
allowed  to  fall  into  water  they  sink  to  the  bottom.  In  some  cases  the 
protoplasm  contains  a  considerable  quantity  of  fat;  so  that,  although 
the  substratum  of  protoplasm  is  heavier  than  water,  the  floating  of  the 
cell  is  due  to  the  lighter  specific  gravity  of  the  fat-particles  overcom- 
ing the  heavier  specific  gravity  of  the  protoplasm. 

The  chemical  composition  of  protoplasm  (a  living  substance)  can 
be  obtained  only  after  it  has  been  killed.  However  paradoxical  this 
may  seem,  it  is  found  impossible  to  apply  the  methods  of  chemistry 
without  killing  it.  Every  reagent  that  comes  in  contact  with  it  dis- 
turbs and  changes  it  and  eventually  kills  it.  Thus,  our  ideas  of  the 


10  PHYSIOLOGY. 

chemical  composition  of  living  protoplasm  are  the  ideas  we  get  from 
the  chemical  composition  of  dead  protoplasm. 

The  substances  of  which  it  is  composed  are : — 

1.  Water. — Water  is  that  element  in  living  substance  that  gives 
it  its  liquid  nature,  allowing  its  particles  to  move  about  with  a  certain 
degree  of  freedom.     In  the  cell,  water  occurs,  either  chemically  com- 
bined with  other  constituents  or  in  the  free  state.     Salts  occur  dis- 
solved in  the  water.     Protoplasm  is  semifluid,  and  about  three-fourths 
of  its  weight  is  due  to  water.     The  molecules  of  protoplasm  are 
thought  to  be  separated  from  one  another  by  layers  of  water. 

2.  Proteids. — The  proteids  take  a  very  active  and  essential  part 
in  the  functions  of  all  cells.     The  proteids  consist  of  the  elements 
carbon,  hydrogen,  sulphur,  nitrogen,  and  oxygen.     Proteids  occur  both 
in  the  protoplasm  and  in  the  nucleus,  but  with  this  difference:    that 
found  in  the  nucleus  has  combined  with  it  phosphoric  acid,  forming 
the  so-called  nucleins.     To  show  this  fact  is  very  easy,  for  the  nuclein 
of  cells  resists  the  action  of  digestion  by  the  gastric  juice.     All  kinds 
of  cells  in  artificial  gastric  juice  have  their  protoplasm  digested  and 
only  the  nuclei  remain;    that  is,  nuclein.     If,  now,  this  nucleus  is 
treated  with  stains,  it  shows  that  the  nuclear  bodies  consist  of  nuclein, 
while  the  protoplasm  of  the  cell  is  constructed  from  other  albuminous 
bodies. 

Protoplasm  is  composed  principally,  then,  of  simple  proteids  and 
compound  proteids  that  lack  phosphorus.  Our  most  common  and 
typical  type  of  an  albuminous  substance,  or  proteid,  is  the  white  of  an 
egg.  This  contains  12  per  cent,  of  actual  proteid  substance,  the 
remainder  being  chiefly  water.  The  albumins  are  the  only  bodies  that 
can  safely  be  said  to  be  found  in  all  cells.  Although  the  albumins 
contain  only  five  elements, — C,  H,  N,  S,  and  0, — yet  the  number  of 
their  atoms  often  exceeds  a  thousand. 

3.  Various  Other  Substances  occur  in  smaller  proportions  as  car- 
bohydrates;   as  glycogen  in  protoplasm  of  liver-cells;    fats,  seen  in 
protoplasm  as  fats  or  oil-drops ;  and  simpler  substances  which  are  the 
result  of  decomposition  of  the  proteids  or  are  concerned  in  its  forma- 
tion.    Also,  inorganic  salts,  such  as  phosphates,  and  chlorides  of  cal- 
cium, sodium,  and  potassium. 

NUCLEUS. 

From  an  examination  of  the  protoplasm  we  pass  on  to  the  nucleus. 
As  we  have  said  before,  "a  cell  is  a  mass  of  protoplasm  containing  a 
nucleus."  Various  properties  and  functions  of  an  important  nature 


THE  CELL.  11 

have  been  assigned  to  protoplasm,  but  it  is  found  that  the  nucleus  is 
equally  as  important.  The  classical  experiments  of  the  old  observers 
upon  protoplasm  gave  them  the  belief  that  the  protoplasm  was  the 
embodiment  of  all  the  functions  of  life.  To  them  the  nucleus  was 
unessential  as  regards  the  activities  of  life.  The  ruling  power  of  the 
protoplasm  was  dismissed  when  it  was  found  that  the  nucleus  in  repro- 
duction of  cells  by  division  or  impregnation  underwent  extraordinary 
changes,  while  the  protoplasm  remained  passive  and  quiet.  Within 
recent  years  there  has  set  in  a  reaction,  and  the  happy  mean  'twixt 
the  two  extremes  is  now  held  to  be  correct:  the  two  are  of  equal 
importance. 

By  extended  research  and  with  staining  reagents  such  as  carmin, 
hsematoxylin,  etc.,  a  distinct  nucleus  was  found  imbedded  in  the  pro- 
toplasm of  most  animal  cells.  For  a  long  time,  and  until  the  micro- 
scope was  greatly  improved,  two  classes  of  organisms  appeared  to  be 
the  exceptions.  They  were :  monera,  the  lowest  and  simplest  organ- 
isms, and  bacteria.  Gradually  the  number  of  each  class  was  reduced 
until  at  the  present  day  it  may  safely  be  said  that  every  cell  contains 
a  distinct  nucleus.  Every  cell  may  thus  be  said  to  be  characterized  by 
two  general  cell-constituents,  protoplasm,  and  at  least  one  nucleus, 
sometimes  more. 

The  form  of  the  nucleus  is  different  in  various  cells.  Usually 
it  is  a  round  or  oval  body  situated  in  the  middle  of  the  cell.  Its 
rounded  form  is  considerably  expanded  in  young  cells,  as  the  ovaries 
in  their  evolution.  Very  frequently  the  form  of  the  element  influences 
that  of  the  nucleus.  Thus,  in  muscle-  and  nerve-  cells  the  nucleus  is 
generally  elongated.  In  the  lower  organisms  it  sometimes  assumes  the 
shape  of  a  horseshoe  or  a  twisted  strand,  or  is  very  much  branched,  the 
processes  running  out  in  every  direction  into  the  surrounding  proto- 
plasm. 

The  size  of  the  nucleus  is  usually  in  proportion  to  the  mass  of 
protoplasm  enveloping  it.  Thus,  in  the  large  ganglion-cells  of  the 
spinal  cord  the  nuclei  are  correspondingly  large.  Also  in  cells  en- 
gaged in  active  work  the  nuclei  are  generally  of  good  size,  as  the 
secreting  cells  of  the  salivary  and  mucous  glands. 

As  to  the  number  of  nuclei  present  in  a  cell  the  general  condition 
seems  to  prevail  of  the  presence  of  but  one  in  a  cell.  There  are  excep- 
tions, however,  as  liver-cells  very  frequently  contain  two,  and  the 
immense  cells  of  bone-marrow  many. 


12  PHYSIOLOGY. 

General  Substance,  or  Structure. 

The  nucleus  is  no  more  of  a  homogeneous  nature  than  the  proto- 
plasm and  presents  several  distinct  substances  and  structures.  The 
different  constituents  that  are  known  are  not  always  present  in  all 
cells  at  all  times  or  in  the  same  proportions.  Among  some  cells  one 
element  may  be  very  conspicuous,  while  in  some  others  it  is  scarcely 
to  be  found.  According  to  Verworn,  the  following  substances  occur 
most  constantly:  (1)  nuclear  sap,  (2)  achromatic  nuclear  substance, 
(3)  chromatic  nuclear  substance,  and  (4)  the  nucleolus. 

The  nuclear  sap  may  be  present  in  large  or  smaller  quantities  and 
is  the  liquid  ground-substance  which  fills  up  the  interstices  left  among 
the  solid  nuclear  constituents.  In  many  cells  under  the  influence  of 
certain  reagents  and  even  in  life  it  is  known  to  be  of  a  very  fine 
granular  nature. 

The  achromatic  nuclear  substance  is  a  structure  of  fine  threads 
found  in  the  nuclear  sap  and  is  characterized,  as  is  also  the  latter,  by 
not  staining  with  the  usual  reagents :  carmin,  hsematoxylin,  etc.  It 
contains  achromatin. 

The  chromatic  nuclear  substance,  as  its  name  implies,  has  an 
affinity  for  coloring-matter  in  the  form  of  different  stains.  It  is 
usually  in  the  form  of  a  continuous  network,  but  sometimes  appears  in 
small  granules,  or  particles.  It  contains  chromatin. 

The  nucleolus,  if  it  appears  at  all,  is  found  in  the  network  of  the 
nucleus  as  a  rounded  or  irregularly  shaped  body.  It  contains  para- 
nuclein  and  has  an  especial  affinity  for  color  and  stains  more  deeply 
than  the  network.  The  nucleoli  are  thought  to  be  passive  bodies  that 
hold  in  reserve  different  constituents  which  are  essential  to  the  life  of 
the  nucleus. 

Sometimes  the  nucleus  is  enveloped  in  a  membrane,  called  the 
nuclear  membrane,  which  marks  it  distinctly  from  the  protoplasm. 
This,  however,  as  with  the  cell-membrane,  is  not  universal  and  is  not 
classed  as  a  general  constituent  of  the  nucleus.  The  sharpness  of  the 
contour  which  distinguishes  the  nucleus  in  the  midst  of  protoplasm 
led  many  histologists  firmly  to  believe  that  the  nucleus  always  does 
possess  a  membrane.  The  truth  is  between  the  two  extreme  opinions. 
The  nucleus  can  very  readily  exist  without  one. 

A  portion  of  a  cell  deprived  of  its  nucleus  may  live  for  a  time,  but 
it  evinces  no  activities  or  functions  other  than  that  of  movement.  It 
neither  absorbs  food  nor  grows  or  reproduces,  but  seems  gradually  to 
dwindle  away  and  die.  From  this  it  is  believed  that  the  nucleus  exer- 


THE  CELL. 


13 


cises  some  powers  with  regard  to  the  building  up  or  constructive  meta- 
morphosis. 

Eegarded  chemically,  the  nucleus  is  composed  principal!)'  of 
proteid  and  a  substance  like  proteid  which  contains  as  much  as  10  per 
cent,  of  phosphorus.  No  doubt  there  are  others,  but  even  the  most 
delicate  chemical  reagents  kill  the  constituents  and  so  lessen  the  oppor- 
tunities for  careful  investigation. 

CENTROSOME. 

About  twenty  years  ago,  when  nuclear  cell-division  was  being 
investigated,  a  small  body  other  than  the  nucleus  was  noticed  during 
the  division  of  the  cell  and  which  was  called  by  various  names:  polar 
corpuscle,  central  corpuscle,  or  centrosome.  The  last  name  seems  to 
be  more  generally  used  at  the  present  time. 

The  centrosome  in  its  simplest  form  is  a  body  of  extreme  minute- 
ness, frequently  not  larger  than  a  microsome,  but  which  exerts  an 
active  influence  on  the  protoplasmic  structure  during  cell-division. 

Because  of  its  influence  in  the  cell  it  has  aroused  more  interest 
among  investigators  than  any  other  component  of  the  cell.  By  some 
it  is  considered  to  be  a  part  of  the  nucleus  and  by  others  of  the  proto- 
plasm. As  a  rule,  it  lies  in  the  protoplasm  just  outside  of  the  nucleus, 
even  during  the  resting  stage,  and  in  certain  conditions  of  the  cell  is 
clearly  indicated  by  a  radiation  of  protoplasm,  the  fibers  of  which  are 
arranged  in  the  form  of  a  star,  the  centrosome  being  at  the  center. 

In  size  the  centrosome  ranges  between  that  of  the  ordinary  micro- 
some  and  the  smallest  micro-organism.  No  structure  has  been  as  yet 
discovered  in  it.  It  cannot  be  classed  as  a  general  cell-constituent, 
since  many  forms  of  the  cell  and  unicellular  organisms  have  been 
examined  and  no  centrosome  found,  due  probably  to  the  inadequacy 
of  the  microscope. 

The  centrosome  does  not  absorb  the  ordinary  stains  suitable  for 
the  nucleus,  but  requires  acid  aniline  dyes,  as  acid  fuchsin  and  orange. 
By  them  it  is  colored  vividly. 

As  a  rule,  there  is  one  centrosome  in  a  cell,  lying  close  to  the 
nucleus  and  surrounded  by  a  raylike  or  rodlike  structure  of  the  proto- 
plasm. As  the  cell  prepares  for  division,  the  centrosome  divides  into 
two  distinct  parts,  both  lying  passively  within  the  starlike  network. 
When  the  daughter-cells  are  examined  each  is  found  to  possess  one  of 
the  centrosomes,  which,  as  the  cell  grows,  passes  through  the  same 
process  as  its  antecedents.  The  centrosome  is  regarded  as  the  par- 
ticular organ  of  cell-division. 


14  PHYSIOLOGY. 

| 

PROTOPLASMIC  MOVEMENT. 

The  movements  of  protoplasm  are  movements  in  currents  and 
the  amoeboid  movement.  In  certain  vegetable  cells  protoplasm  moves 
and  causes  a  true  rotation  of  its  substance,  as  in  chara;  or  the  move- 
ment may  be  in  opposite  direction  and  the  paths  even  cross  over  each 
other.  In  this  movement  all  parts  of  the  protoplasm  do  not  move 
with  the  same  rapidity.  The  rate  in  protoplasm  is  about  1/50  inch 
per  minute. 

Movements  differ  according  to  whether  the  protoplasm  is  naked 
—without  any  enveloping  membrane — or  inclosed  within  a  firm  wall, 
or  membrane. 


Fig.  3. — Amoeba  Proteus.     (LEIDY.) 

n,  Nucleus,     cv,  Contractile  vacuole.     N,  Food-vacuoles.     en,  Endoplasm. 
ek,  Ectoplasm. 

1.   Movement  of  the  Naked  Protoplasm. 

Probably  our  most  common  and  typical  form  of  naked  protoplasm 
is  presented  to  us  by  the  fresh-water  amoeba,  found  in  stagnant  water. 
The  amoeba  is  a  unicellular  organism,  about  1/100o  incn  in  diameter, 
possessing  one  or  more  nuclei,  and  which  is  almost  continually  in 
motion,  due  to  its  extending  numerous  protoplasmic  projections,  called 
pseudopodia  (false  feet) .  It  then  rolls  its  entire  mass  into  the  pseudo- 
podium,  or  fingerlike  projection,  only  to  continue  the  same  operation 
repeatedly  during  its  life. 

The  pseudopodia  assume  different  forms  and  shapes  in  the  differ- 
ent kinds  of  cells,  and  in  this  way  the  identity  of  a  cell  is  frequently 


THE  CELL. 


15 


aided  by  an  observation  of  the  processes.  For  example,  most  of  the 
fresh-water  amoeba  possess  broad,  lobate  or  finger-shaped  pseudopodia ; 
leucocytes,  white  blood-corpuscles,  divided  and  pointed  pseudopodia; 
some  of  the  rhizopods  and  pigment-cells,  threadlike  and  reticular 
pseudopodia  which  flow  into  one  another. 

In  the  human  body  some  of  the  cells — such  as  white  blood- 
corpuscles,  lymph-corpuscles  and  connective-tissue  cells — possess  move- 
ments, which,  because  of  their  likeness  to  those  of  the  amoeba,  are 
called  amoeboid. 

2.  Ciliary  Movement. 

There  have  been  discovered  cells  and  unicellular  organisms  which 
possess  delicate,  hairlike  processes  which  extend  in  greater  or  less 
numbers  from  their  surfaces.  They  are  called  flagella,  or  cilia. 
These  resemble  very  thin  pseudopodia  when  they  are  composed  of 
hyaloplasm  alone,  as  the  cilia  and  flagella  are  homogeneous  and 
nongranular  in  nature.  However,  they  differ  from  pseudopodia  in 
that  their  movements  are  very  energetic  and  always  definite,  and 
also  that,  unlike  pseudopodia,  their  structures  are  not  temporary, 
but  permanent,  being  neither  protruded  nor  withdrawn.  The  ciliary 
cells  lining  the  trachea  are  subjects  for  examination.  The  deep 
back  part  of  the  throat  of  a  frog  is  gently  scraped  and  the  scrapings 
placed  upon  a  warm  stage  in  a  drop  of  water.  When  we  examine 
the  cells  under  the  microscope  we  see  upon  their  surface  a  constant 
rapid  movement,  but  the  movement  is  so  rapid  that  we  see  only  the 
motion,  and  not  the  vibrating  cilia.  If,  however,  the  vibrations  be 
lowered  to  about  a  dozen  per  second,  we  are  then  able  to  see  the 
cilia  themselves.  Ciliary  movements  are  of  various  kinds.  Most 
often  it  is  a  movement  of  elevation  and.  depression  of  the  cilia ;  some- 
times it  is  like  the  extension  and  flexion  of  our  fingers,  at  other  times 
a  sort  of  wave  or  whirlpool-like  movement.  In  these  movements  all 
the  cilia  on  the  surface  move  in  the  same  direction  like  a  field  of  grain 
before  the  wind.  Each  completed  movement  of  the  cilia  is  composed 
of  two  movements  of  unequal  duration,  the  longer  corresponding  to 
contraction  and  the  shorter  to  relaxation  of  the  cilia.  Ciliary  move- 
ments may  be  of  a  high  rapidity,  as  many  as  960  to  about  1000  per 
minute,  and  entirely  independent  of  the  circulation  and  the  nervous 
system.  These  movements  are  able  to  continue  after  death  as  long  as  a 
day,  while  in  frogs  they  have  been  observed  for  many  days. 

Cilia  are  about  1/BOOO  inch  in  length  and  are  able  to  perform  some 
work.  By  their  movements  they  are  able  to  float  a  cell  in  a  liquid, 


16  PHYSIOLOGY. 

such  as  water,  even  though  the  cell  and  the  cilia  are  composed,  in  a 
great  part,  of  protoplasm,  whose  specific  gravity  is  heavier  than  water 
and  naturally  inclined  to  sink,  and  at  the  same  time  they  propel  the 
cell  in  some  definite  direction  at  a  much  faster  speed  than  that 
obtained  by  the  protrusion  and  retraction  of  pseudopodia.  The  func- 
tion of  the  ciliated  cells  does  not  appear  to  be  of  any  particular 
importance  in  man  except  that  in  the  trachea  their  movements  bring 
to  the  larynx  foreign  substances  that  have  been  inhaled  into  the  lungs, 
such  as  dust,  etc.,  and  to  bring  up  for  expectoration  the  thickened 
mucus  that  is  formed  during  the  stages  of  a  cold. 

A  practical  illustration  of  the  effects  of  the  protoplasmic  move- 
ments of  leucocytes  (white  blood-corpuscles)  can  be  observed  when  an 
injury  occurs  to  any  part  of  the  body.  As  a  result  of  the  injury  and 
as  an  attempt  at  repair,  more  blood  is  sent  to  the  injured  part.  This, 
called  congestion,  gives  to  it  its  red  color.  With  the  additional 
quantity  of  blood  comes  an  additional  number  of  leucocytes.  They 
by  protoplasmic  movements,  pass  through  the  walls  of  the  capillaries 
to  the  seat  of  the  injury  to  take  up  dead  portions.  Sometimes  bac- 
teria lodge  in  the  wound,  which  the  leucocytes  approach  and  kill  by 
ingestion,  as  it  were,  thus  rendering  them  harmless.  This  process  of 
ingesting  bacteria  and  other  foreign  substances  is  called  phagocytosis, 
and  hence  the  leucocytes  are  sometimes  termed  phagocytes. 

Chemotaxis  is  the  phenomenon  of  a  leucocyte  in  active  movement, 
which  by  one-sided  action  of  the  chemical  products  of  bacteria,  as 
toxins,  moves  toward  (positive)  or  away  (negative)  from  the  bacteria. 

CELL=DIVISION. 

We  have  learned  that  organs  are  composed  of  various  structures, 
called  tissues.  A  tissue  may  be  defined  as  "a  group  of  similar  cells 
having  a  similar  function."  For  example,  muscular  tissue  is  made  up 
of  ribbonlike  muscle-cells;  mucous  tissue  of  secreting,  goblet-shaped 
cells ;  nervous  tissue  of  ganglion-cells,  with  their  numerous  projecting 
dendrons,  etc. 

By  observation  we  notice  a  variety  of  tissues  due  to  a  diversity  of 
kinds  of  cells ;  also  that  all  tissues  of  a  kind  are  not  necessarily  of  the 
same  bulk,  size,  or  weight. 

The  chick  shortly  after  its  exit  from  the  shell  contains  in  its 
body  a  number  of  organs  of  a  definite  size  and  consistency.  It  has  a 
head,  limbs,  muscles,  heart,  lungs,  intestines,  liver,  etc.  We  see  that 
these  organs,  of  course,  are  of  a  size  and  weight  in  proportion  to  its 


THE  CELL.  17 

age— none  of  them  large  or  heavy.  Upon  examination,  the  tissues 
of  the  various  organs  would  be  found  to  be  composed  of  cells  such  as 
we  would  expect  them  to  contain;  that  is,  the  muscles  of  muscle-cells, 
the  bones  of  osseous  cells,  the  brain  of  ganglion-cells,  etc.  Further- 
more, although  cells  are  of  different  sizes  and  forms,  yet  there  is  very 
little  difference  between  the  cells  of  a  particular  tissue  as  compared 
with  one  another  or  with  those  of  the  adult  animal  in  respect  to  size, 
for  the  size  of  every  cell  is  definite. 

When  we  observe  the  same  animal  one  year  from  its  birth,  we 
notice  some  striking  differences:  it  is  much  larger  and  heavier,  the 
various  organs  are  fuller,  more  compact,  and  show  the  effects  of  the 
development  which  took  place  as  it  approached  maturity.  The  head, 
brain,  muscles,  heart,  lungs,  intestines,  etc.,  are  all  much  larger  and 
better  developed  than  those  found  in  the  small  chick.  However,  if  a 
microscopical  examination  be  made  of  the  various  tissues  in  this,  the 
adult  animal,  what  do  we  find  and  how  do  the  cells  compare  with  those 
of  the  chick  ?  Nothing  remarkable  in  the  individual  cells  themselves. 
The  liver-cells  of  the  adult  are  no  larger  than  those  of  the  chick,  nor 
the  ganglion-,  muscle-,  or  other  cells.  What  we  do  perceive  is  a  great 
increase  in  the  number  of  the  cells  in  any  particular  tissue.  The  liver 
and  brain  of  the  adult  animal  contain  many  more  cells  than  the  same 
respective  organs  of  the  chick.  Thus  we  see  that  there  has  been  a 
growth  due,  not  to  larger  cells,  but  a  greater  number  of  cells.  That  is, 
the  cells  have  multiplied. 

Similarly,  as  the  infant  passes  through  the  various  stages  of  boy- 
hood, youth,  and  manhood,  we  say  that  he  grows,  for  there  is  an 
increase  in  the  size  and  weight  of  the  various  organs  of  his  body.  This 
means  that  there  is  a  greater  number  of  cells  composing  the  tissues 
of  his  various  organs.  The  power  to  multiply — that  is,  producing  new 
forms  similar  to  itself — is  one  of  the  most  important  and  characteristic 
functions  of  the  cell.  By  this  attribute  it  not  only  is  able  to  maintain 
its  own  particular  kind  or  species,  but  also  can  undergo  constructive 
metamorphosis:  building  up  or  growing  until  any  part  or  organ  is 
matured. 

A  cell  multiplies  by  dividing  into  two  or  more  parts.  Each  part 
is,  of  course,  smaller  than  the  original  or  mother-cell,  but  by  assimilat- 
ing nutrient  material  from  the  surrounding  tissues  it  grows  until  each 
part  is  the  size  of  the  mother-cell,  when  it  also  is  ready  for  division,  or 
reproduction. 

Xo  cell  exists  but  that  had  its  origin  in  some  pre-existing  cell. 
In  animals  whose  tissues  are  composed  of  many  cells  those  same  tissues 


18  PHYSIOLOGY. 

can  be  traced  back  to  single  cells  of  which  they  are  developments.  The 
animal  itself,  with  all  its  many  and  various  parts  and  structures, 
originated  from  a  single  cell.,  the  germ-cell,  or  ovum,  which  is  also 
part  of  a  cell  having  existed  in  the  parent-body. 

Schleiden,  the  botanist  and  accredited  discoverer  of  the  cell- 
theory  among  plants,  and  Schwann,  to  whom  Schleiden  confided  his 
views  and  ideas  of  plant-structure  and  who  then  reduced  animal  tissues 
to  their  structural  units,  the  cells,  were  anxious  to  know  the  origin 
of  the  cells.  To  them  the  presence  of  the  nucleus  was  known  and 
even  the  nucleolus,  but  their  instruments  were  not  powerful  enough 
to  allow  of  their  penetrating  deeper  and  getting  the  correct  ideas  of 
cell-division. 

It  was  proved  in  1858  that  cells  multiplied  as  a  result  of  the  divi- 
sion of  the  two  equally  essential  parts  of  the  cell,  the  nucleus  and 
protoplasm.  Our  present  conception  that  the  two  are  of  equal  im- 
portance and  value  dates  from  this  time.  It  was  asserted  that  the 
division  began  within  and  proceeded  to  the  outer  parts  of  the  cell. 
That  is,  the  nucleolus  was  divided,  its  division  was  followed  by  separa- 
tion of  the  nucleus,  and  this  in  turn  followed  by  constriction  and 
division  of  the  protoplasm  with  its  enveloping  membrane.  These 
views  were  confirmed  by  Virchow,  who  formulated  the  doctrine  "Omnis 
cellula  e  cellula"  (every  cell  from  a  cell). 

Later  it  was  discovered  by  the  investigation  of  some  of  the 
tissue-cells  that  the  process  of  division  was  not  so  simple  as  expected. 
In  some  cases  it  was  found  that  the  nucleus  became  star-shaped,  or 
lobed,  or  even  seemed  to  disappear  altogether  before  cell-division.  A 
few  years  later  it  was  seen  that  the  process  of  division  was  complicated 
in  the  extreme  and  that  the  cell-nucleus  underwent  a  variety  of  trans- 
formations, assuming  different  shapes  and  figures  until  two  daughter- 
cells  were  formed  from  the  mother-cell.  This  process  was  afterward 
named  Jcaryokinesis. 

By  experiment  it  was  demonstrated  that,  if  a  cell  in  a  living 
organism  or  tissue  was  so  divided  that  one  of  the  parts  was  composed 
of  protoplasm  only,  none  of  the  nucleus  being  present,  the  protoplasmic 
part  continued  to  live  for  a  considerable  time,  but  that,  of  the  vital 
phenomena  exhibited  by  the  normal  cell,  it  possessed  only  that  of 
movement.  It  was  unable  to  take  up  from  the  surrounding  tissues  a 
proper  amount  of  nutrition  and  that  growth  and  reproduction  never 
occurred.  After  a  time  it  died.  Thus  it  was  concerned  only  in 
destructive,  not  constructive,  metamorphosis.  It  was  totally  unable 
to  build  itself  up,  grow,  and  reproduce  others  of  its  species.  On  the 


THE  CELL. 


19 


other  hand,  the  part  containing  the  nucleus  grew  and  reproduced  its 
kind,  forming  daughter-cells,  who  in  turn  formed  other  cells,  etc. 

Thus,  in  order  that  the  daughter-cells  may  possess  the  same 
properties,  form,  and  functions  of  the  mother-cell, — in  fact,  in  order 
that  it  may  live, — it  becomes  necessary  in  the  division  that  both  the 
nucleus  and  the  protoplasm  must  divide.  The  disposition  of  any  cell 
to  divide  or  reproduce  is  usually  announced  by  changes  in  its  nucleus, 
both  physical  and  chemical.  In  fact,  the  division  of  any  cell  is  pre- 
ceded by  division  of  the  nucleus.  This  process  in  the  cells  of  most 
organisms  is  very  complicated,  whereas  the  division  of  the  protoplasm 
is  most  simple,  consisting  of  the  appearance  of  a  constriction,  which 
becomes  deeper  and  deeper,  forming  a  groove,  or  fissure,  until  event- 
ually the  mass  is  divided  into  two  parts. 

The  evident  importance  of  the  relation  of  the  nucleus  to  cell- 
division  has  led  to  extended  study  of  the  nucleus  and  its  transforma- 
tions during  the  process  of  reproduction,  with  the  result  that  upon  its 
functions  in  this  respect  three  forms  of  division  are  recognized:  (1) 
direct  cell-division,,  (2)  indirect  cell-division,  and  (3)  endogenous 
nuclear  multiplication. 

1.   Direct  Cell=di vision  (Amitosis). 

Direct  cell-division  is  very  rare  and  present  in  only  some  of  the 
unicellular  organisms  and  leucocytes.  In  pathological  formations, 
however,  such  as  tumors,  this  form  of  division  occurs  very  frequently. 
To  get  a  better  conception  of  the  direct  form  of  division  we  will  study 
one  of  the  infusorians,  the  typical  amceba,  and  the  changes  occurring 
in  it  during  reproduction.  The  first  intimation  of  a  division  is  noted 
in  the  spherical  nucleus,  which  becomes  elongated,  the  middle  por- 
tion of  it  being  indented  by  a  constriction  which  gives  to  the  nucleus 
a  dumb-bell  shape.  The  constricted  portion  becomes  gradually  nar- 
rower and  slenderer  until  the  two  heads  of  the  ball  separate  and 
each  assumes  the  same  shape  as  its  mother — spherical.  The  cell  thus 
contains  two  distinct  nuclei.  Following  the  division  of  the  nucleus 
is  that  of  the  protoplasm  by  constriction  also.  The  indentation  always 
appears  between  the  two  nuclei.  Eventually  two  cells  are  thus  formed, 
each  with  a  separate  nucleus;  each  daughter-cell  is,  of  course,  smaller 
than  its  mother,  but  by  the  assimilation  of  the  nutrient  material  sur- 
rounding it  it  soon  grows  to  the  normal,  definite  size.  This  process 
often  requires  several  hours  for  its  completion,  the  various  stages  fre- 
quently being  accomplished  in  an  uncertain  manner. 


20  PHYSIOLOGY. 

2.   Indirect  CelNdivision  (Mitosis,  or  Karyokinesis). 

By  far  the  greater  number  of  animal  and  plant-  cells  follow  the 
more  complicated  and  intricate  method  of  indirect,  or  ~karyokinetic, 
form  of  division.  The  division  of  the  protoplasm  is  simple  enough, 
following  only  the  laws  of  constriction  until  the  mass  is  completely 
separated  into  two  parts  by  means  of  a  furrow,  or  fissure.  It  is  the 
nucleus  which  undergoes  very  remarkable  and  typical  changes,  very 
complicated  in  their  nature,  but  which  in  plants  and  animals  are  con- 
stant and  agree  very  much  in  regard  to  essentials.  Thus  the  indirect 
method  is  very  nearly,  though  not  quite,  universal. 

As  a  cell  prepares  for  division  the  most  evident  and  important 
fact  noticed  is  a  change  in  its  nucleus,  both  physical  and  chemical. 
The  nucleus  becomes  somewhat  enlarged  and  its  chromatic  nuclear 
substance,  or  chromoplasm, — so  called  because  it  has  an  affinity  for 
stains, — begins  to  become  changed  little  by  little  from  the  netlike 
arrangements  of  its  minute  granules  and  particles  until  the  substance 
is  arranged  in  the  form  of  threads  loosely  rolled  up,  like  a  coil  or 
convolution,  called  the  slcein,  or  spirem.  These  consist  principally 
of  nuclein,  and  stain  more  deeply  than  the  surrounding  parts,  and 
are,  hence,  more  easily  discerned.  It  is  the  presence  of  these  threads 
that  gives  to  the  process  the  name  mitosis.  In  most  cases  there 
is  but  a  single  thread  that  is  coiled  or  convoluted  throughout  its 
entire  length;  occasionally  there  occur  several  such  threads.  The 
threads  are  somewhat  thicker  than  before  and  more  separated  than 
during  the  resting  stage.  With  the  formation  of  the  spirem,  or 
wreath,  the  nucleoli  and  membrane,  if  any,  disappear.  In  some  cases 
the  nucleoli  are  dissolved  and  cast  into  the  hyaloplasm,  where  they 
degenerate  and  have  no  further  function. 

The  thread  of  the  spirem  becomes  divided  transversely  into 
nearly  equal  parts,  or  bodies,  known  as  chromosomes,  which  in  most 
cases  are  in  the  form  of  rods,  straight  or  curved.  The  ground - 
substance  of  the  nucleus  now  becomes  a  part  of  the  surrounding  hyal- 
oplasm. The  chromosomes  at  first  are  placed  rather  irregularly,  but 
they  soon  begin  to  arrange  themselves  into  a  more  definite  form,  that 
of  a  rosette.  The  curved  chromosomes  now  become  more  angular  and 
V-shaped,  the  angle  pointing  toward  the  center  of  the  nuclear  space 
while  the  free  ends  are  directed  toward  the  circumference,  this  figure 
being  called  the  aster,  or  garland.  While  in  the  form  of  the  aster 
each  chromosome  splits  longitudinally  into  halves,  so  that  we  have 
just  again  as  many,  though  thinner,  chromosomes. 


THE  CELL.  o-j 

Before  the  membrane  has  been  dissolved  there  appear  in  the  pro- 
toplasm, but  very  near  the  nuclear  membrane,  two  small  granules 
lying  side  by  side.  These  are  the  centrosomes.  They  are  of  a  sub- 
stance that  stains  with  difficulty.  Gradually  they  begin  to  separate 
from  one  another,  moving  in  a  semicircle,  until  they  are  diametrically 
opposite  one  another,  or  at  the  nuclear  poles.  As  they  have  been  in 
motion  the  nuclear  membrane  has  been  dissolving,  so  that  by  the  time 
they  are  again  at  rest  the  membrane  has  disappeared.  The  achromatic 
nuclear  spindle  develops  between  the  centrosomes.  When  they  begin 
to  separate  the  spindle  is  small,  scarcely  discernible,  and  like  a  band  in 
form.  As  the  centrosomes  separate  more,  the  fibers  become  more 
plainly  visible  and  assume  the  form  of  a  spindle — broad  in  the  middle 
and  converging  at  either  end,  toward  and  ending  in  the  centrosomes. 
The  protoplasm  now  arranges  itself  around  the  centrosomes  in  the 
form  of  rays  as  a  star,  as  though  the  filaments  of  protoplasm  were 
attracted  by  the  centrosomes  in  the  manner  of  iron  filings  by  a  magnet. 
At  first  these  fibers  are  small,  but  increase  in  length  and  numbers  as 
the  division  of  the  cell  progresses  until  they  run  throughout  the  entire 
protoplasmic  mass. 

The  V-shaped  filaments,  called  chromosomes,  are  now  collected  in 
the  plane  of  the  equator,  called  the  equatorial  plate.  While  the 
chromosomes  have  been  arranging  themselves  in  the  plane  of  tin.- 
plate,  they  have  been  growing  somewhat  shorter  and  thicker,  their 
angles  pointing  to  the  axis  of  the  spindle  and  their  ends  to  the  cir- 
cumference. By  the  contraction  of  the  spindle  fibers  the  daughter- 
chromosomes  (the  result  of  the  original  chromosomes  being  divided 
longitudinally  into  two  separate  halves  by  means  of  fission)  are  divided 
into  two  equal  groups,  which  are  moved  toward  the  points,  or  poles,  of 
the  spindle,  but  never  reach  it  absolutely.  Between  these  groups  fine 
"connecting  fibrils"  stretch.  This  figure  is  called  the  double  star,  or 
diaster.  The  star  shape  is  formed  by  the  angles  of  the  chromosomes 
being  arranged  next  to  the  centrosomes  with  their  free  ends  extending 
out  radially. 

There  now  follows  a  retransforming  of  the  daughter-chromosomes 
arranged  in  the  form  of  a  star  into  a  genuine  resting  nucleus.  The 
angles  begin  to  disappear,  the  threads  draw  more  closely  to  one  an- 
other, becoming  more  bent  and  roughened  at  the  same  time  that  little 
processes  appear  on  their  surfaces.  A  very  delicate  nuclear  membrane 
develops  and  surrounds  the  group  of  threads.  The  radiating  fibers 
of  protoplasm  around  the  centrosomes  become  more  and  more  indis- 
tinct until  they  finally  disappear.  The  same  thing  occurs  with  the 
"connecting  fibrils." 


22 


PHYSIOLOGY. 


When  the  two  daughter-stars  were  separated  as  far  as  possible 
there  appeared  on  the  surface  of  the  cell-body  a  fissure,  cutting  into 
the  protoplasm  in  the  line  of  the  equatorial  plate,  until  the  cell  was 
completely  divided  into  two  parts,  eacti  containing  a  nucleus. 

The  duration  of  this  process  has  been  seen  to  take  place  in  man  in 
half  an  hour,  while  in  the  larva  of  the  salamander  it  has  been  known 
to  take  as  long  as  five  hours. 

The  different  stages  are  very  neatly  and  correctly  summarized  and 
tabulated  as  they  appear  in  Quain's  "Anatomy":— 

Network,  or  reticulum  ........    1.  Resting  condition  of  mother-nucleus. 

T    2.  Close  skein  of  fine  convoluted  filaments. 
Skein,  or  spirem  ............  J     3.  Open  skein  of  thicker  filaments.      Spindle 

appears. 

{4.  Movement  of  V-shaped  chromosomes  to 
middle  of  nucleus,  and  each  splits  into 
two  sister-threads. 

C    5.  Stellate    arrangement    of    V    filaments    at 
Star,  or  monaster  ..........  equator  of  gpmdle 


C    6.  Separation    of    cleft    filaments    and    move- 
Divergence,  or  metakmesis.  .  J  „,,  ,      .    ,, 

1  ment  along  fibers  of  spindle. 

C    7.  Convergence   of   V  filaments   toward   poles 
Double  star,  or  diaster  .....   |  of  spindle. 

C    8.  Open  skein  in  daughter-nuclei. 

Double  skein,  or  dispirem  .  .  .  J     _       *          .    .     .      ,        ,  ,  ,  . 

1     9.  Close  skein  in  daughter-nuclei. 

Network,  or  reticulum  ........  10.  Resting  condition  of  daughter-nuclei. 

3.  Endogenous  Nuclear  Multiplication. 

A  third  rare  mode  of  nuclear  multiplication,  to  which  is  given 
the  above-named  title,  was  discovered  in  the  thalassicola. 

The  thalassicola,  which  is  the  largest  in  size  of  the  radiolarians 
and  the  diameter  of  whose  central  capsule  is  nearly  equal  to  that  of 
the  frog's  egg,  has  during  the  major  portion  of  its  life  one  single, 
highly  differentiated,  giant  nucleus,  called  the  internal  vesicle.  This 
nucleus,  or  internal  vesicle,  usually  attains  to  1/50  inch  in  diameter, 
and  possesses  a  thick,  porous,  nuclear  membrane.  It  is  very  similar 
to  the  multinucleated  germinal  vesicle  of  the  ovum  of  an  amphibian. 

Simultaneously  with  the  advent  of  the  centrosome  into  the  proto- 
plasm there  appeared  in  the  latter,  which  heretofore  has  been  entirely 
free  and  clear,  a  large  number  of  very  small  nuclei.  These  act  as 
centers,  around  each  one  of  which  there  develop  nucleated  zoospores, 


THE  CELL.  23 

which  may  amount  finally  to  as  many  as  some  hundreds  of  thousands 
of  separate  cells. 

Fatigue  of  Cells. — Hodge,  of  Clark  University,  has  found  changes 
in  the  cell  corresponding  to  rest  or  activity.  Thus  the  nerve-cell  in 
the  morning  has  a  clear,  round  nucleus,  while  in  the  evening,  being 
tired  from  work,  the  nucleus  has  an  irregular  contour. 

LITERATURE  CONSULTED. 

Verworn,  "General  Physiology/'  1899. 
Hertwig,  "  The  Cell,"  1895. 


CHAPTER  II. 

(a)  CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD. 
(b)  ALIMENTARY  SUBSTANCES. 

DIGESTION  has  been  described  as  the  physical  and  chemical  altera- 
tion of  the  foodstuffs  into  forms  better  fitted  for  absorption  by  the 
action  of  certain  soluble  ferments,  the  digestive  enzymes. 

The  animal  organism  had  its  birth  in  a  single  ovum  or  cell,  which, 
under  certain  favoring  circumstances  and  conditions,  developed  into 
a  mass  of  simple  cells.  As  development  proceeded  this  aggregation 
became  differentiated  into  tissues  by  the  grouping  of  the  cells,  altered 
by  chemical  changes  in  the  substance  of  the  cells  themselves,  by  altera- 
tions in  their  shapes,  and  by  deposits  of  intercellular  substances.  As 
the  organism  continued  to  grow,  the  various  parts  became  more  and 
more  complex  by  use  and  development  until  it  presented  a  highly  com- 
plex unit. 

In  the  metabolism  of  the  cell  it  was  learned  that  the  various  cells 
while  performing  their  various  vital  phenomena  must  constantly 
maintain  a  very  nice  balance  in  respect  to  waste  and  repair.  That  is, 
the  various  kinds  of  cells  took  out  from  their  environments  those  sub- 
stances that  were  necessary  for  their  economy  to  build  themselves  up 
and  grow,  while  the  waste-products  were  excreted.  A  distinctive 
property  of  the  cells  was  the  selective  power  exercised  in  regard  to 
different  nutrient  materials  with  which  they  came  into  contact.  Al- 
though the  surrounding  media  might  contain  many  kinds  of  food,  yet 
cells  of  a  particular  kind  took  only  that  for  themselves  which  was  best 
adapted  to  their  wants,  disregarding  entirely  all  the  others.  As  there 
was  a  great  variety  of  cells,  there  must  necessarily  be  a  corresponding 
variety  of  foodstuffs. 

What  is  true  of  the  cells  is  true  of  that  of  which  they  are  but 
components  or  units:  the  body.  Among  the  phenomena  produced 
by  the  waste  of  the  solid  constituents  of  the  body  and  the  loss  of  the 
fluid  or  watery  parts  of  the  tissues  are  the  sensations  of  hunger  and 
thirst.  These  sensations  of  appetite  excite  the  desire  to  take  food, 
which  by  the  processes  of  digestion  is  prepared  for  absorption  and  cir- 
culation in  the  blood  to  supply  the  various  needs  of  the  organism. 

The  term  food  includes  all  those  substances  received  into  the 
(24) 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  25 

alimentary  canal  and  used  for  the  support  of  life  by  supplying  the 
waste  continually  occurring  in  the  living  animal  tissues,  and  also 
weight,  heat,  and  energy.  Food  contains  substances  that  have  a  cer- 
tain chemical  relation  to  the  tissues  which  it  supports.  The  substances 
out  of  which  the  complex  adult  tissues  are  constructed  or  built  up  are 
chemical  elements,,  chemical  compounds,  or  unions  of  these  elements. 
The  food  taken  in  by  the  animal  consists  of  the  same  or  similar  com- 
position, in  its  nature  very  complex. 

Animals  are  either  carnivorous  or  herbivorous.  The  carnivora, 
or  flesh-eating  species,  consume  food  possessing  apparently  the  same 
chemical  components  as  the  tissues  and  fluids  of  their  own  bodies.  The 
food  of  the  herbivora,  or  vegetable-eating  species,  contains  principles 
resembling  very  closely  those  found  in  the  animal  body.  No  matter 
what  the  source  or  nature  of  the  food  for  animals  might  be,  their 
chemical  constituents  or  principles  are  similar,  since  it  is  through  the 
agency  of  the  vegetable  kingdom  with  the  aid  of  light  and  heat  from 
the  sun  that  the  simpler  combinations  of  inorganic  nature  are  woven 
together  and  elaborated  to  form  the  complex  organisms  in  the  shape 
of  plants  and  vegetables.  Thus,  the  animal  kingdom  is  dependent 
on  the  vegetable  for  its  existence,  as  numerous  experiments  have 
proven  that  the  animal  organism  does  not  possess  the  power  to  any 
great  extent  of  constructing  complex  from  simple  materials.  Yet 
complex  foods  it  must  have  to  supply  its  own  complex  constituents. 
However,  it  is  also  necessary  that  the  food  should  possess,  besides  the 
complex  constituents,  a  proper  proportion  of  the  various  principles, 
and  these  must  be  in  a  digestible  form.  It  is  well  known  that  beans, 
peas,  and  other  vegetables  contain  a  very  considerable  percentage  of 
proteid,  but  it  is  in  such  indigestible  form  that  much  of  it  passes  off 
in  the  faeces.  The  various  digestive  juices  had  been  unable  properly 
to  dissolve  their  nutritious  elements. 

Of  the  74  elements  known  to  the  chemist,  but  20  are  found  in  the 
body.  They  are:  carbon,  hydrogen,  nitrogen,  oxygen,  sulphur,  phos- 
phorus, fluorin,  chlorine,  iodine,  silicon,  sodium,  potassium,  calcium, 
magnesium,  lithium,  iron,  and  occasionally  manganese,  copper,  and 
lead.  These  elements  are  rarely  found  in  the  free  state,  being  usually 
in  the  form  of  compounds. 

The  compounds,  or,  as  they  are  sometimes  termed,  -proximate 
principles,  are  divided  into:  (1)  mineral,  or  inorganic,  compounds; 
(2)  organic  compounds,  or  compounds  of  carbon.  The  organic  com- 
pounds may  again  be  divided  very  conveniently  into  two  groups :  the 
nitrogenous  and  nonnitrogenous. 


26  PHYSIOLOGY. 

The  inorganic  compounds  are  water;  the  various  acids,  such  as 
the  hydrochloric  acid  of  the  gastric  juice;  and  numerous  salts. 

Since  the  proximate  principles  of  both  food  and  the  body  are  the 
same,,  mention  of  them  will  be  known  to  refer  to  both.  A  very  con- 
venient method  of  grouping  the  principles  of  both  food  and  the  body 
is  that  by  Halliburton,  as  follows  :— 

r  Water. 
Inorganic <   ganS}  as  chlorides  and  phosphates  of  sodium  and  calcium. 

f  Proteids:  albumin,  myosin,  etc. 
Nitrogenous...  J   Albuminoids:  gelatin,  keratin;  etc. 

I   Simpler  nitrogenous  bodies:    lecithin,  urea,  etc. 

C  Fats:   butter,  adipose  tissue. 
Nonnitrogenous  J    Carbohydrates:    sugar,  starch. 

1   Simple  organic  bodies:    alcohol,  lactic  acid. 

Although  all  of  these  elements  are  present,  yet  not  all  are  of 
equal  importance  or  occur  in  the  same  proportions.  Among  the  inor- 
ganic group,  water  and  salts  are  prominent;  among  the  organic,  carbo- 
hydrates, fats,  and  proteids. 

WATER. 

Water  forms  more  than  one-half  of  the  body-weight.  The  value 
of  water  to  the  economy  can  be  readily  appreciated  by  the  student 
when  he  considers  that  the  various  processes  and  stages  of  digestion, 
absorption,  and  assimilation  are  dependent  upon  hydration  and  dehy- 
dration. About  fifty  ounces  of  urine  are  excreted  daily,  this  being 
the  main  avenue  for  the  escape  of  watery  elements  from  the  body.  In 
addition,  considerable  water  is  given  off  by  the  skin  as  sensible  and 
insensible  perspiration,  while  expired  air  is  heavily  laden  with 
moisture. 

With  so  much  water  making  its  escape  from  the  body,  at  least 
as  much  must  find  its  way  into  the  economy.  About  two  and  a  half 
quarts  of  water  are  ingested  daily  as  food.  The  water  we  drink  ought 
to  be  fresh,  limpid,  without  smell,  and  of  an  agreeable  taste.  When 
complete  and  exact  analysis  is  impossible,  the  taste  is  the  only  safe 
criterion  or  judge  as  to  its  fitness.  Drinking-water  should  always  con- 
tain a  certain  percentage  of  air.  The  palatability  is  due  to  the  pres- 
ence of  carbonic  acid  gas  in  the  water.  Besides  gaseous  constituents, 
solid  substances  are  also  present.  These  are  both  mineral  and  or- 
ganic, and  should  be  present  in  but  very  small  amount. 

Somewhat  more  water  is  excreted  daily  than  is  ingested,  since 
some  water  is  formed  in  the  tissues  by  the  oxidation  of  hydrogen. 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  37 

SALTS. 

The  most  important  salts  found  are  the  sulphates  and  chlorides 
of  sodium;  the  phosphates  of  sodium,  potassium,  calcium,  and  mag- 
nesium ;  and  the  carbonates  of  sodium  and  calcium. 

Of  these  various  salts,  sodium  chloride  is  the  most  important  and 
the  most  common  one  found.  In  the  fluids — blood,  serum,  lymph,  and 
urine — this  salt  is  high  in  percentage.  While  in  the  body  it  favors 
absorption  by  increasing  the  endosmosis  of  the  tissues  and  so  aids 
metabolic  processes,  the  absence  of  sodium  chloride  for  an  extended 
time  causes  disturbances  and  disorders  in  the  constitution.  There  are 
about  3000  grains  of  common  salt  present  in  the  body.  About  225 
grains  are  excreted  daily  in  the  urine,  while  some  finds  its  exit  as  a 
component  of  the  faces,  sweat,  and  tears. 

A  practical  illustration  of  its  value  to  animal  life  may  be  gained 
by  noticing  how  wild  animals  repair  to  the  so-called  "salt-licks"  at 
various  times,  traveling  for  many  miles  to  procure  it. 

Calcium  phosphate  is  a  very  prominent  factor  of  the  mineral 
solids  of  the  body.  It  forms  about  one-half  of  the  bony  skeleton, 
where  it  is  most  abundant,  although  it  occurs  to  some  extent  in  all 
other  solids  and  fluids.  This  salt  is  particularly  conspicuous  in  milk. 

Iron  is  an  important  element  of  haemoglobin.  It  is  this  iron 
in  the  red  blood-corpuscles  that  is  the  means  of  holding  the  oxygen 
without  being  itself  oxidized.  A  want  of  it  causes  the  pathological 
condition  called  anasmia.  In  the  blood  of  an  adult  are  found  forty- 
five  grains.  In  small  proportions  it  is  found  in  the  liquids  of  the 
body, — as  the  chyle,  lymph,  bile,  urine,  etc., — in  the  fseces,  and  traces 
in  the  liver  and  spleen. 

CARBOHYDRATES. 

The  carbohydrates  are  found  principally  in  the  vegetable  king- 
dom. They  are,  however,  not  indigenous  to  the  vegetable  kingdom, 
but  are  found  and  formed  in  animal  tissues;  notably,  glycogen,  or 
animal  starch ;  dextrose ;  and  lactose,  or  milk-sugar. 

For  the  sake  of  a  clearer  conception  of  the  term  carbohydrate  the 
components  of  the  name  are  used  when  it  is  defined  as  a  compound  of 
carbon,  hydrogen,  and  oxygen,  the  last  two  in  the  proportion  occurring 
in  the  formation  of  water,  two  to  one. 
The  carbohydrates  are: — 

Glucoses  (CeHjA),  or  monosaccharides. 
Saccharoses  (C12H22On)»  or  disaccharides. 
Amyloses  (CaH1005)n,  or  polysaccharides. 


o8  PHYSIOLOGY. 

The  Glucoses  are  glucose;  dextrose,,  or  grape-sugar;  lasvulose, 
and  gala  close.  The  glucoses  have  three  properties  which  are  im- 
portant for  the  physiologist  to  know:  physical,  chemical,  and  bio- 
logical. From  the  fact  that  it  deviates  the  plane  of  polarization  to  the 
right,  its  physical  property  is  demonstrated,  whence  its  name,  dextrose. 
Its  chemical  property  is  the  reducing  of  certain  metallic  salts  in  the 
presence  of  alkalies.  Biologically,  it  ferments  under  the  influence 
of  yeast  to  form  carbonic  acid  and  ethylic  alcohol. 

Saccharoses. — The  saccharoses  are  saccharose,  or  cane-sugar;  lac- 
tose, or  milk-sugar ;  and  maltose.  When  saccharose,  or  cane-sugar,  is 
boiled  with  a  dilute  mineral  acid,  the  right-handed  polarizing  solution 
of  saccharose  is  transformed  into  invert-sugar,  or  is  said  to  be  inverted. 
Invert-sugar  is  a  mixture  of  equal  weights  of  glucose,  a  right-handed 
polarizing  agent,  and  laevulose,  which  is  a  left-handed  polarizing  body. 
The  saccharoses  do  not  reduce  the  copper  salts.  The  saccharoses  are 
not  directly  fermentable  by  yeast  except  in  this  way :  ( 1 )  when  yeast 
is  added  the  saccharoses  take  up  water  and  the  soluble  ferment  of 
yeast,  invertin,  changes  the  saccharoses  into  glucose  and  laevulose; 
then  (2)  the  vital  fermentation  of  the  glucose  and  lasvulose  by  the 
yeast-cell. 

Lactose,  or  sugar  of  milk,  is  a  right-handed  polarizing  sugar.  It 
reduces  the  copper  salts,  but  is  not  fermentable  either  directly  or  in- 
directly by  the  yeast-ferment.  Lactose  ferments  in  the  presence  of 
the  lactic  acid  bacillus  to  form  lactic  acid. 

Maltose  is  a  right-handed  polarizing  sugar,  reduces  copper  salts, 
and  ferments  by  yeast.  Maltose  has  the  same  properties  as  glucose, 
but  is  distinguished  in  two  ways:  (1)  the  light-rotating  power  of 
glucose  is  56  degrees,  while  maltose  is  150  degrees;  (2)  the  reducing 
of  metallic  salts  by  glucose  is  equal  to  100,  while  that  of  maltose  is 
but  66.  *  The  sugar  in  blood  is  a  glucose. 

By  moistening  barley  and  germinating  it  in  heaps  at  a  constant 
temperature,  the  starch  of  the  barley  is  converted  into  dextrose  and 
maltose.  This  change  is  brought  about  by  the  ferment  called  diastase, 
which  is  found  in  barley.  This  product  when  dried  is  denominated 
malt,  which  when  it  is  acted  upon  by  yeast  produces  the  malted  bever- 
ages, beer  and  ale.  Maltose  by  invertin  of  yeast  is  changed  into 
glucose. 

Amyloses,  or  Polysaccharides.— Under  the  influence  of  dilute 
mineral  acids  the  amyloses  are  changed  by  boiling  or  are  transformed 
into  glucose.  Starch  presents  a  polarizing  cross :  a  black  cross  upon  a 
white  ground  or  a  white  cross  upon  a  black  ground.  Starch  does  not 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD. 


29 

reduce  copper  solution  nor  is  it  fermentable  by  yeast.     When  iodine 
is  added  to  starch  it  gives  a  blue  color. 

Glycogen,  or  animal  starch,  does  not  reduce  copper  salts  nor  is 
it  fermentable  by  yeast.  During  the  hydrolysis  of  starch  dextrin  is 
formed  as  an  intermediate  product.  Dextrins  colored  red  by  iodine 
are  called  erythrodextrins ;  those  not  colored  by  iodine  are  called 
achroodextrins. 

FATS. 

Fats  form  a  more  or  less  variable  proportion  of  the  animal 
economy.  They  come  to  us  principally  in  the  form  of  animal  articles 
of  food,  but  to  some  extent  in  vegetable  food  also,  especially  in  seeds, 
nuts,  fruit,  and  roots. 

The  fats  contain  in  their  substances  a  fatty  principle  having 
acid  properties — a  sort  of  fatty  acid.  When  acted  upon  by  alkalies 
and  ferments  this  acid  becomes  separated  and  a  sweet  principle  known 
as  glycerin  makes  its  appearance.  Thus  fats  may  be  said  to  be  com- 
pounds of  fatty  acids  with  glycerin.  It  would  seem,  however,  that 
the  glycerin  had  not  pre-existed  in  the  fats,  as  the  united  weight  of 
the  glycerin  and  fatty  acid  produced  exceeds  that  of  the  fat  originally 
employed. 

In  bone-marrow,  adipose  tissue,  and  milk  the  fats  are  very  promi- 
nent components.  The  adipose  tissue  consists  of  nucleated  vesicles 
filled  with  fatty  matter.  The  vesicles  are  closely  packed  together 
and  surrounded  by  a  network  of  blood-vessels  which  draw  out  from 
this  source  a  supply  for  nutrition.  This  fatty  tissue  is  found  between 
the  muscles,  bones,  vessels,  etc.,  and  by  its  accumulation  under  the 
skin  gives  to  the  surface  of  the  body  its  full  and  regular  outline. 

By  reason  of  its  bad  conducting  power  it  helps  to  keep  the 
various  structures  of  the  body  warm  by  a  coating  of  it  lying  under  the 
skin.  This  fact  is  best  illustrated  in  the  warm-blooded  aquatic  ani- 
mals, as  the  seal,  porpoise,  and  whale. 

The  normal  fats  found  in  the  body  and  used  for  food  are  divided 
into  three  compounds :  stearin,  palmitin,  and  olein. 

Stearin  is  the  most  solid  of  the  three.  It  is  typically  illustrated 
in  mutton  suet,  and  is  the  element  which  makes  this  fat  so  hard  and 
firm  and  characterizes  it  at  once.  Its  melting-point  is  145°  F.,  so 
that  at  ordinary  temperatures  it  is  solid. 

Palmitin  occupies  a  position  midway  between  stearin  and  olein  as 
regards  consistency.  It  is  the  principal  constituent  of  most  animal 
fats  and  occurs  largely  in  vegetable  fats  also. 


30  PHYSIOLOGY. 

Olein  is  always  found  in  a  fluid  state  unless  the  temperature  be 
very  low.  When  the  olein  ingredients  predominate  in  a  body  it  is  then 
in  a  liquid  state,  as  in  the  case  of  the  oils.  Olein  is  found  in  both 
animal  and  vegetable  fats,  but  the  vegetable  fats  are  richer  in  it  than 
the  animal.  The  oils  used  in  food — olive-oil,  oil  of  sweet  almonds,  etc. 
— are  derived  from  the  vegetable  kingdom. 

Human  fat  contains  about  75  per  cent,  of  olein  plus  a  small  quan- 
tity of  fatty  acids  in  a  free  state.  All  are  soluble  in  hot  alcohol,  ether, 
and  chloroform,  but  insoluble  in  water. 

Saponification. 

When  fat  is  boiled  with  alcoholic  soda  or  potash,  the  particles  of 
fat  are  broken  up  into  a  small  quantity  of  glycerin  and  a  larger  quan- 
tity of  fatty  acid.  The  fatty  acid  unites  with  the  soda  or  potash,  form- 
ing, as  a  result,  soap.  This  process  of  soap-forming  is  known  as 
Saponification. 

Emulsification. 

If  oil  and  water  are  well  shaken  together  the  fatty  particles  do 
not  form  a  part  of  the  water,  but  are  held  in  suspension  and  come 
to  the  surface  in  the  form  of  small  globules.  A  mixture  of  an  oil, 
a  soap,  and  water  is  spoken  of  as  an  emulsion.  No  emulsion  is  per- 
manent, for  even  in  milk,  the  most  perfect  of  emulsions,  the  fatty 
particles  in  the  form  of  cream  rise  to  the  surface  in  a  few  hours. 
Emulsification  is  a  physical  or  mechanical  rather  than  a  chemical 
change.  Both  soaps  and  emulsions  are  continually  being  formed  in 
the  body  during  the  digestion  of  fats. 

PROTEIDS. 

The  principal  constituents  forming  the  muscular,  nervous,  and 
glandular  tissues,  as  well  as  the  serum,  blood,  and  lymph,  are  proteids. 
In  normal  urine  there  are  found  no  proteids,  or,  if  any,  only  traces. 
In  a  great  measure  the  various  phenomena  of  life  are  present  and  due 
to  the  protoplasm  in  the  cells.  On  analyzing  protoplasm  chemically 
its  substance  is,  of  course,  killed  by  the  reagents  used,  but  there 
invariably  result  in  the  process  proteids.  Whether  the  proteids  exist 
as  such  in  the  protoplasm  or  occur  only  after  the  death  of  the  proto- 
plasm has  not  been  fully  established,  but  are  believed  to  be  the  con- 
stituents of  it.  However,  none  of  the  phenomena  of  life  occur  without 
their  presence. 

Proteids   are  very   complex,   comprising   compounds   of   carbon, 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  31 

hydrogen,  nitrogen,  oxygen,  and  sulphur.  They  may  be  either  solid  or 
liquid,  as  they  are  found  in  the  different  tissues  of  the  body.  The 
different  classes  of  proteids  present  both  physical  and  chemical  pecul- 
iarities, although  all  have  certain  common  reactions.  Some  are 
soluble,  others  are  insoluble,  in  water,  while  nearly  all  are  soluble  in 
ether  and  alcohol.  Strong  acids  and  alkalies  are  also  capable  of  dis- 
solving the  proteids,  but  in  the  process  of  dissolution  decomposition 
almost  invariably  occurs. 

The  supply  of  proteids  in  our  bodies  is  obtained  from  the  vege- 
table kingdom,  being  taken  in  as  vegetables  directly,  or  indirectly  in 
the  form  of  meat  which  is  derived  from  animals  that  live  on  vegetables. 
Thus  the  proteids  are  built  up  from  the  simpler  inorganic  compounds 
taken  from  the  soil  and  air  and  elaborated  in  plant-structure. 

The  chemical  composition  of  the  proteids  is  variable,  depending 
upon  the  products  analyzed  by  the  different  investigators,  as  the  purity 
of  the  substances  cannot  be  definitely  determined.  From  investiga- 
tions we  have  the  following  average  percentages:  0,  21.50  to  23.50; 
H,  6.5  to  7.3;  N,  15.0  to  17.6;  C,  50.6  to  54.5;  S,  0.3  to  2.2. 

The  nitrogen  and  sulphur  are  each  contained  in  the  molecule  in 
two  forms,  the  one  loosely  combined,  the  other  firmly  combined. 
The  basis  of  construction  of  all  proteids  is,  according  to  Kossel,  a  body 
called  protamin  (C30H57N1706),  which  on  hydrolysis  gives  three  basic 
substances  each  containing  six  carbon  atoms,  hence  called  hexone 
bases,  lysin,  histidin,  and  arginin.  Protamin  has  been  found  loosely 
combined  with  nucleic  acid  in  the  spermatozoa  of  fishes.  In  the  pro- 
teid  molecule  it  is  firmly  combined  with  the  amido  acids,  like  leucin, 
glycin,  and  usually  with  aromatic  bodies,  like  tyrosin,  etc.,  and  inor- 
ganic elements,  like  sulphur  and  phosphorus.1 

Classification  of  Proteids. 

For  the  sake  of  convenience  and  study  the  proteids  have  been 
divided  into  various  groups  and  classes  by  different  authorities.  They 
are  almost  universally  divided  into  the  two  main  groups  of  animal  and 
vegetable  origin.  The  amount  of  proteid  matter  in  plants,  particu- 
larly the  full-grown  ones,  is  less  than  in  animals.  It  is  found  dis- 
solved in  their  juices,  in  the  protoplasm,  or  deposited  in  the  form  of 
grains  called  aleuron  granules.  Vegetable  proteids  are  divisible  into 
the  same  classes  as  the  animal,  but,  since  human  physiology  deals  with 
animal  proteids,  the  vegetables  are  disregarded. 


Beddard,  "Practical  Physiology." 


32  PHYSIOLOGY. 

A  convenient  classification  is  into:  (1)  native  albumins,  (2) 
derived  albumins,  or  albuminates,  (3)  compound  proteids,  (-i)  globu- 
lins, (5)  peptones,  and  (6)  albuminoids. 

1.  Native  Albumins. 

The  proteids  of  this  class  are  those  that  are  found  in  an  unaltered, 
natural  state  or  condition  in  the  solids  of  the  body.  They  are  soluble 
in  water  and  are  not  precipitated  by  the  dilute  acids.  The  two  main 
forms  are  egg-albumin  and  serum-albumin.  The  egg-albumin  occurs 
in  the  part  of  the  egg  known  as  the  white.  The  serum-albumin  is 
found  not  only  in  the  blood-serum,,  but  also  in  the  lymph  as  it  is 
found  in  its  proper  lymphatic  channels  and  diffused  throughout  the 
tissues,  in  the  chyle,  milk,  and  transudations. 

2.  Derived  Albumins,  or  Albuminates. 

To  this  class  belong  two  divisions:  acid-albumin  and  alkali- 
albumin. 

The  derived  albumins  are  formed  from  the  native  albumins  by 
the  action  of  weak  alkalies  or  acids.  Thus,  when  a  native  albumin, 
such  as  serum-albumin,  is  treated  for  a  while  with  dilute  hydrochloric 
acid  its  properties  become  entirely  changed.  The  solution  is  no  longer 
able  to  be  coagulated  by  heat,  and  when  the  solution  is  carefully  neu- 
tralized the  whole  of  the  proteid  is  thrown  down  as  a  precipitate. 
The  substance  into  which  the  native  albumin  was  changed  by  the 
action  of  an  acid  is  called  an  acid-albumin,  or  syntonin.  This  acid- 
albumin  is  insoluble  in  distilled  water  and  neutral  saline  solutions,  but 
readily  soluble  in  dilute  acids  and  alkalies.  This  is  the  process 
through  which  albumins  pass  when  undergoing  gastric  digestion  and 
when  acted  upon  by  the  HC1  of  the  gastric  juice. 

If  serum-albumin,  egg-albumin,  or  washed  muscle  is  acted  on  by 
an  alkali,  instead  of  an  acid,  the  proteid  undergoes  changes  similar  to 
those  produced  by  the  acid,  except  that  the  product  formed  is  an 
alkali-albumin  instead  of  an  acid  one. 

3.  Compound  Proteids. 

These  are  native  proteids  with  another  organic  substance,  in  con- 
trast to  albuminates,  which  are  compounds  of  native  proteids  with 
inorganic  substances.  The  compound  proteids  include  (1)  gluco- 
proteids,  like  mucin,  consisting  of  a  proteid  combined  with  a  carbo- 
hydrate group;  (2)  pseudonuclein,  like  casein  of  milk,  nuclein  of 
cell  nuclei  and  a  nucleo-proteid,  vitellin  of  yelk  of  eggs;  (3)  histones, 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  33 

made  up  of  albumin  and  protamin.  To  the  histones  belong  globin,  the 
proteid  which  is  separated  from  haemoglobin  by  decomposing  it  with 
acids  and  alkalies,  and  a  pigment  called  hsematin,  which  contains  0.4 
per  cent,  of  iron. 

4.  Globulins.  , 

The  globulins  are  quite  abundant.  The  globulins  differ  from  the 
albumins  in  that  they  are  not  soluble  in  distilled  water.  There  must 
be  present  an  appreciable  amount  of  sodium  chloride  or  magnesium 
sulphate. 

The  different  members  of  this  group  are :  Serum-globulin  (para- 
globulin),  and  fibrinogen  in  blood,  myosinogen  in  muscle,  etc. 

Paraglobulin  is  a  precipitate  that  can  be  formed  from  blood- 
serum  by  diluting  it  tenfold  with  water  and  passing  through  it  a 
current  of  carbon  anhydride.  A  flocculent  and  finally  a  granular 
precipitate  results,  which  is  the  paraglobulin. 

The  coagulated  proteids  are  fibrin,  myosin,  and  casein.  The 
coagulation  is  produced  by  ferments. 

Fibrinogen  is  present  in  the  blood,  chyle,  serous  fluids,  and 
transudations. 

Myosinogen  is  the  principal  proteid  found  in  muscle. 

5.  Peptones. 

In  the  body  peptones  are  the  final  results  of  the  action  of  the  gas- 
tric and  pancreatic  juices  upon  the  native  proteids;  and  as  peptones 
are  ready  for  absorption  by  the  cells.  Although  formed  in  large  quan- 
tities in  the  stomach  and  intestine,  they  are  quickly  absorbed  as  soon 
as  formed,  since  none  is  left  in  these  organs.  Peptones  can,  however, 
be  produced  outside  the  body  by  the  action  of  dilute  acids  at  medium 
temperatures. 

The  peptones  are  soluble  in  water,  not  coagulated  by  the  presence 
of  heat,  can  be  precipitated  by  the  usual  proteid  precipitants,  and 
diffused  very  readily  through  membranous  tissues. 

Intermediate  products  between  the  native  proteids  and  peptones 
are  the  proteoses.  True  peptones  are  not  found  in  the  circulating 
juices  of  plants,  but  the  product  found  is  very  likely  proteose.  The 
proteoses  are  only  slightly  diffusible,  are  not  coagulated  by  heat,  but 
can  be  precipitated.  A  characteristic  feature  of  their  precipitates  is 
that  they  can  be  dissolved  by  heating,  but  reappear  when  the  solution 
cools. 


34:  PHYSIOLOGY. 

6.  Nitrogenous  Bodies  Allied  to  Proteids,  or  Albuminoids. 

Besides  the  proteids  there  are  other  nitrogenous,  noncrystalline 
bodies  that  are  allied  to  the  former,  having  many  general  points 
in  common. 

Gelatin  is  the  substance  produced  by  heating  the  collagen,  of 
connective-tissue  fibers,  in  dilute  acetic  acid  for  several  days.  It  pos- 
sesses the  property  of  setting  into  a  jelly  when  its  concentration  is 
greater  than  1  per  cent.  When  digested  it  is  converted  into  a  peptone, 
and,  although  readily  absorbed,  is  not  able  to  take  the  place  of  a  true 
proteid,  since  it  cannot  build  up  nitrogenous  tissue,  being  valuable 
only  as  a  means  of  storing  up  energy. 

Keratin  is  the  horny  material  forming  the  outer  layer  of  the 
epidermis,  hair,  wool,  nails,  hoofs,  etc. 

Elastin  of  elastic  tissue  belongs  to  this  group. 

ALIMENTARY   SUBSTANCES. 

We  have  learned  that  the  body  is  composed  of  the  chemical  con- 
stituents or  proximate  principles,  carbohydrates,  fats,  and  proteids 
comprising  the  organic  group,  and  water  and  salts  the  inorganic  class. 
In  order  that  the  nutrition  of  the  body  may  proceed  normally,  it  is 
very  apparent  that  those  principles  must  be  supplied  in  the  food,  in 
the  proper  proportions  and  quantities.  So,  a  proper  diet  for  man  is 
one  containing  the  proximate  principles  in  their  proper  proportions, 
the  value  of  it  depending  mainly  on  the  amount  of  carbon  and  nitro- 
gen present. 

The  elements,  as  elements,  are  not  valuable;  it  is  only  when 
they  are  in  combination  that  they  serve  their  proper  ends  as  foods. 
For  the  elements  must  be  united  previously  by  some  living  organism 
to  constitute  an  organic  product.  It  is  not  often  that  the  alimentary 
substances  are  used  by  us  as  Nature  furnishes  them,  even  though  they 
contain  the  proper  ingredients.  One  requisite  is  that  they  should 
be  presented  in  a  digestible  form.  Water,  heat,  and  condiments  are 
the  three  agents  used  to  make  food  more  palatable  and  digestible. 
Water  helps  to  soften  the  insoluble  substances  and  to  dissolve  the 
principal  substances.  Heat  modifies  the  foods  still  more,  so  that  they 
acquire  different  characters.  The  condiments  give  physical  satisfac- 
tion and  enjoyment,  and  at  the  same  time  they  please  the  taste. 

A  diet  to  be  sufficient  must  be  adapted  to  the  particular  indi- 
vidual's need,  keeping  in  mind,  also,  the  climate,  age  of  person,  and 
the  amount  of  work  done  by  him. 


ALIMENTARY  SUBSTANCES.  35 

Although  we  make  changes  of  clothing  to  suit  the  weather  condi- 
tions in  order  that  the  body  may  not  suffer  in  regard  to  the  surrounding 
temperature,  yet  our  diet  is  also  regulated  with  the  same  ends  in  view. 
In  cold  weather  we  eat  more,  to  furnish  an  extra  amount  of  heat ;  in 
warm  weather  we  eat  less  than  usual.  A  growing  youth's  body  must 
not  only  repair  the  daily  waste,  but  also  assist  in  constructive  meta- 
morphosis, or  growth,  so  that  he  requires  relatively  more  food  per 
diem  than  the  adult.  Because  of  the  waste  attending  action,  the 
workingman  requires  more  than  the  ordinary  supply  of  food. 

There  are  some  single  foods  which  contain  all  the  necessary  proxi- 
mate principles  in  proper  proportions,  but  they  are  the  exceptions 
rather  than  the  rule.  Thus,  milk  and  eggs  are  classed  as  perfect  foods. 
It  is  usually  necessary  for  a  proper  diet  to  contain  a  variety  of  sub- 
stances in  this  list. 

For  a  man  doing  a  moderate  amount  of  work,  it  has  been  com- 
puted that  it  is  necessary  that  the  daily  diet  should  contain  the  fol- 
lowing amounts : — 

Proteid 125  grams. 

Fat    50  grams. 

Carbohydrates 500  grams. 

Alimentary  substances  comprise  products  of  both  animal  and 
vegetable  kingdoms.  The  principal  ones  are  animal  substances,  with 
cereals,  potatoes,  drinks,  condiments,  cocoa,  coffee,  tea,  etc. 

The  animal  substances,  or  foods,  comprise:  (1)  meat,  (2)  eggs, 
and  (3)  milk,  with  its  derivatives — cream,  butter,  and  cheese. 

The  parts  of  animals  used  for  food  are  the  various  portions  of 
their  muscular  system.  They  comprise  the  general  term  meat.  Ani- 
mal food,  being  identical  with  the  body  structures,  requires  nothing  to 
be  added  or  detracted  to  make  it  fit  to  give  proper  nourishment. 

MEAT. 

The  more  compact  the  fiber,  the  less  digestible  the  meat.  Hence 
ham  is  much  less  digestible  than  other  meats.  The  more  fat  that  is 
combined  intimately  with  the  fibers,  so  much  less  is  the  digestibility 
of  the  meat,  because  the  fat  melts  and  coats  the  fibers  of  the  meat  with 
a  layer  of  oil  which  prevents  the  ferment  from  acting  upon  it.  Meat 
is  noted  for  the  large  quantity  of  nitrogenous  matter  which  it  contains, 
having  four  times  the  amount  of  proteid  compared  with  the  same 
weight  of  milk.  The  proteid  in  meat  is  myosin,  the  main  constituent. 

Beef-tea  is  a  solution  of  gelatin,  salts,  extracted  matters,  a  little 
albumin,  together  with  some  fat.  The  value  of  beef-tea  as  an  all- 


36  PHYSIOLOGY. 

mentary  substance  has  been  much  disputed,  some  claiming  great  results 
from  it,  others  none.  However,  one  thing  is  certain :  it  possesses  a 
stimulant  and  restorative  value,  though  it  must  not  be  depended  upon 
as  a  food  and  administered  as  such. 

The  process  of  cooking  meat  loosens  up  the  various  fascise  and 
enveloping  membranes,  thereby  separating  the  fibers;  at  the  same 
time  parasitic  growths  are  killed.  Thus  the  digestive  juices  are  given 
a  greater  opportunity  for  acting  upon  all  parts  of  the  foods,  even 
penetrating  into  the  innermost  parts. 

EGGS. 

The  white  of  an  egg  is  a  faint-yellowish,  albuminous  fluid  inclosed 
in  a  framework  of  thin  membranes,  and  this  fluid  itself  is  very  liquid, 
but  seems  viscid  because  the  membranes  are  entangled.  Ovalbumin, 
or  the  egg-albumin  of  the  egg-white,  is  the  chief  constituent.  The 
mineral  bodies  in  the  white  of  egg  are  potash,  soda,  lime,  magnesia, 
iron,  chlorine,  phosphoric  acid,  and  sulphuric  acid. 

The  principal  part  of  the  yelk  is  an  orange-yellow,  alkaline  emul- 
sion of  a  mild  taste.  The  yelk  contains  vitellin  as  its  principal  con- 
stituent. Besides  vitellin,  the  yelk  contains  alkali  albuminate  and 
albumin.  The  yelk,  besides  vitellin,  contains  a  phosphorized  fat  (leci- 
thin) with  cholesterin,  fats,  and  a  small  quantity  of  sugar  and  of 
mineral  bodies,  chiefly  lime  and  phosphoric  acid. 

As  the  egg  is  so  easily  digested  it  is  prized  highly  as  a  food. 
However,  the  more  that  an  egg  is  boiled,  the  more  insoluble  do  the 
proteids  become  and  so  are  more  indigestible. 

In  cases  where  eggs  are  difficult  of  digestion  the  white  of  egg 
may  be  given.  The  yelks  of  eggs  make  some  persons  have  headache 
and  drowsiness.  The  caloric  value  of  two  eggs  is  about  twenty  calories, 
equal  about  to  the  heat-value  of  a  tumbler  of  milk. 

MILK. 

Like  eggs,  milk  contains  all  the  elements  necessary  for  the  main- 
tenance of  life,  and  hence  it  is  regarded  as  a  type  of  alimentary  sub- 
stances and  classed  as  a  perfect  food.  It  serves  very  well  as  an 
infant-food. 

The  quantitative  composition  of  cows'  milk  and  human  milk  is 
as  follows,  according  to  Bunge : — 

PROTEID.     FAT.        CARB°-      SALT 

HYDRATE. 

Cows'  milk    3.5  3.7  4.9  0.7 

Human  milk  .  1.7  3.4  6.2  0.23 


ALIMENTARY  SUBSTANCES.  37 

The  amount  of  fat  and  carbohydrate  is  nearly  the  same  in  both, 
there  being,  however,  twice  as  much  proteid  and  nearly  three  times  as 
much  salt  in  cows'  as  in  human  milk.  To  bring  cows'  milk  to  the 
same  condition  as  human  milk  it  is  necessary  to  dilute  with  an  equal 
amount  of  water  and  at  the  same  time  to  add  some  cream  and  sugar. 

Milk  is  a  watery  solution  of  various  proteids,  a  carbohydrate  and 
salt,  containing  in  suspension  emulsified  fat.  Cows'  milk  is  an 
opalescent  solution  with  a  characteristic  taste  and  an  amphoteric  reac- 
tion. The  specific  gravity  varies  between  1.028  and  1.034.  Micro- 
scopically, it  consists,  like  blood,  of  plasma  and  corpuscles,  or  globules, 
of  fat.  Boiling  does  not  coagulate  fresh  milk,  but  forms  a  skin  on  its 
surface  which  is  chiefly  composed  of  caseinogen  inmeshing  some  fat- 
particles.  This  film  is  formed  by  the  drying  of  proteid  at  the  surface 
of  the  milk.  The  chief  proteid  of  milk  is  a  pseudonuclein  called 
caseinogen,  and  can  be  precipitated  by  adding  to  the  diluted  milk  a 
weak  acid  or  by  saturating  it  with  a  neutral  salt.  The  chief  pecul- 
iarity of  caseinogen  is  its  coagulating  power  when  treated  with  a  fer- 
ment, rennin,  in  the  presence  of  lime  salts.  The  coagulation  of  milk 
depends  upon  the  change  of  a  soluble  proteid,  caseinogen,  into  an 
insoluble  body,  casein,  by  means  of  the  enzyme,  rennin,  and  the  pres- 
ence of  lime  salts  is  necessary.  It  is  probable  that  the  rennin  first 
splits  the  caseinogen  into  two  bodies,  the  more  important  being  soluble 
casein,  which  then  combines  with  the  calcium  salts  to  form  a  caseinate 
of  calcium,  while  the  other  passes  into  solution  in  the  whey  as  whey 
proteid,  or  lactoserum  proteose. 

The  casein  thus  generated  inmeshes  the  fat-granules  and  forms 
milk-curd.  This  curd,  like  the  blood-clot,  shrinks  after  a  few  hours 
and  an  opalescent  fluid,  or  serum,  called  whey,  is  expressed. 

This  whey  contains,  besides  the  whey-proteid,  or  lactoserum  pro- 
teose, traces  of  other  proteids  and  also  lactose  and  milk  salts.  The 
casein  of  cows'  milk  forms  large  masses  on  coagulation,  while  women's 
milk  forms  very  fine  flakes. 

The  lactose,  or  sugar  of  milk,  does  not  readily  ferment  with  yeast, 
but  is  capable  of  undergoing  a  special  fermentation,  by  which  it  is 
changed  by  the  lactic  acid  bacillus  into  lactic  acid,  and  this  lactic  acid 
is  further  split  up  into  butyric  acid.  These  two  acids,  lactic  and 
butyric,  precipitate  the  caseinogen  and  produce  the  curd  in  sour  milk ; 
but  this  curd  is  quite  a  different  body  from  that  produced  by  rennin, 
for  it  can  be  dissolved  by  a  weak  alkali,  and  then  the  rennin  will  clot 
it.  Potassium  oxalate,  which  precipitates  the  calcium  in  the  milk, 
prevents  the  clotting  of  milk.  The  other  proteids  in  milk  besides 
caseinogen  are  lactalbumin  and  lactoglobulin. 


38 


PHYSIOLOGY. 


Kumyss  is  mares'  milk  fermented.  It  contains  10  per  cent,  of 
solids,  3  per  cent,  of  alcohol,  2  per  cent,  of  fat,  2  per  cent,  of  sugar,  1 
per  cent,  of  lactic  acid,  1  to  2  per  cent,  of  casein,  and  1  volume  per 
cent,  of  carbonic  acid. 

Kephir  is  cows7  milk  fermented  by  kephyr  grains. 

Matzoon  is  prepared  by  adding  to  milk  a  ferment  consisting  of 
some  form  of  yeast  and  the  lactic  acid  bacilli.  It,  however,  contains 
very  much  less  alcohol  and  carbonic  acid  than  kumyss.  Plasmon 
is  prepared  by  precipitating  casein  from  fresh  milk.  Then  it  is  dis- 
solved in  sodium  bicarbonate  in  the  presence  of  free  carbon  dioxide, 
which  prevents  the  alkali  from  decomposing  the  casein.  It  is  then 


Fig.  4. — Specimens  of  Milk,  viewed  through  the  Microscope. 
(LANDOIS.) 

M,    Milk.      C,    Colostrum. 

dried,  and  is  a  yellowish-white  body.  It  contains  2  per  cent,  of  fat 
and  milk-sugar  and  7  per  cent,  of  salts.  It  is  used  as  a  substitute  for 
milk  when  a  large  amount  of  water  is  not  desirable. 

The  fats  of  milk  are  olein,  palmitin,  stearin,  caproin,  and  butyrin. 
The  milk  of  women  contains  twice  as  much  olein  as  palmitin  and 
stearin,  but  they  are  about  the  same  in  quantity  in  cows'  milk.  In 
cows'  milk  two-fifths  is  olein,  one-third  is  palmitin,  one-sixth  stearin 
and  butyrin,  and  caproin  one-fourteenth  of  the  total  fat. 

Buttermilk  contains  about  10  per  cent,  of  solids,  including  casein ; 
lactose;  and  about  1  per  cent,  of  fats. 

Butter  is  formed  by  the  fatty  portions  in  churning  making  the 
fat-particles  adhere  to  each  other,  forming  a  yellow,  fatty  mass. 


ALIMENTARY  SUBSTANCES.  39 

The  salts  of  milk  average  0.6  per  cent,  and  they  consist  chiefly 
of  phosphate  of  lime  with  calcium  chloride,  magnesium  phosphate,  and 
traces  of  iron. 

Milk  also  contains  about  7.6  per  cent,  of  carbonic  acid  and  traces 
of  oxygen  and  nitrogen. 

The  quantity  of  milk  daily  secreted  by  a  woman  is  about  one 
quart. 

The  quantity  of  milk  changes  during  lactation,  which  lasts  in  the 
woman  about  ten  months.  In  the  case  of  the  woman  the  percentage 
of  casein  and  fat  increase  to  the  end  of  the  second  month,  but  sugar 
lessens  even  in  the  first  month.  During  the  fifth  to  the  seventh  month 
there  is  a  diminution  of  fat,  and  between  the  ninth  and  tenth  months 
a  decrease  of  casein.  In  the  first  five  months  the  salts  increase ;  after 
that  they  diminish. 

Colostrum  is  the  milk  secreted  for  a  few  days  after  parturition, 
and  it  has  peculiar  characters.  It  contains  large  corpuscles  called 
colostrum-corpuscles,  which  are  large  cells  full  of  colorless,  fatty  par- 
ticles. 

A  poisonous  principle  is  sometimes  generated  in  milk  by  microbes. 
It  is  called  tyrotoxicon. 

VEGETABLE  FOODS. 

Vegetable  substances  differ  very  much  from  animal  bodies  in  their 
physical  appearances  and  in  some  respects  also  chemically.  The  vege- 
table matters  are  capable  of  being  transformed  into  the  various  animal 
components  and  thereby  nourish  the  animal  body,  since  they  contain 
all  the  elements,  or  proximate  principles,  that  are  necessary  for  the 
maintenance  of  life.  They  need  a  more  complex  apparatus  for  their 
transformation,  and  as  a  consequence  the  digestive  organs  of  the 
herbivora  are  better  developed  and  more  complex  than  those  of  the 
carnivora. 

The  cereals  have  the  same  general  composition,  all  containing  the 
same  proximate  principles,  but  not  all  possess  the  same  relative 
amounts,  because  of  which  some  are  more  valuable  as  food  than  others. 
The  most  important  of  the  cereals  is  wheat. 

Wheat,  as  a  source  of  food,  occupies  a  very  important  place  and  is 
one  of  the  most  widely  cultivated  of  the  cereals.  The  wheat-grains  by 
grinding  have  their  cellulose  coats  burst,  and  the  resulting  powder 
is  called  flour.  This  contains,  on  an  average,  70  per  cent,  of  carbo- 
hydrates, 8  per  cent,  of  proteid,  and  1  per  cent,  of  fat.  The  coverings 
of  the  grain  still  contain  some  albumin  and  starch  and  thus  form 


40  PHYSIOLOGY. 

bran,  a  substance  used  for  feeding  the  herbivora.  Bread  is  made  by 
a  mixture  of  wheat-flour  and  water,  forming  dough.  The  body  which, 
on  the  addition  of  water,  becomes  viscid  is  called  gluten,  and  is  a  tough, 
sticky  mass.  This  is  made  more  porous  by  carbonic  acid,  which  is 
generated  in  the  dough  by  the  action  of  the  yeast-plant  on  sugar.  The 
sugar  is  produced  by  the  diastase  in  the  flour,  which  hydrates  the  starch 
into  sugar.  Baking  kills  the  yeast-action  and  makes  the  vesicles  filled 
with  carbonic  acid  expand,  so  the  dough  is  filled  with  little  cavities. 
The  crust  of  bread  is  formed  by  the  heat  coagulating  the  gluten,  and 
at  the  same  time  the  heat  transforms  the  starch  into  dextrin  and  solu- 
ble starch.  The  glazing  of  the  crust  is  due  to  dextrin.  The  different 
color  of  the  crust  and  its  taste  is  due  to  a  caramel  generated  by  the 
action  of  heat  on  the  sugar  produced  by  the  diastase. 

ACCESSORY  FOODS. 

In  addition  to  the  ordinary  foods  there  is  a  series  of  articles 
which  are  not  necessary  to  the  maintenance  of  life,  but  which  are  fre- 
quently used.  They  are:  alcohol,  tea,  coffee,  and  cocoa.  Of  these 
accessory  foods,  alcohol  is  the  predominant  one  and  is  used  in  a  variety 
of  drinks. 

Alcohol. — Beer  contains  from  3  to  5  per  cent,  of  alcohol.  It  also 
has  from  5  to  7  per  cent,  of  extractives,  which  consist  mainly  of 
dextrin  and  maltose,  with  albumose,  which  give  it  nutrient  properties. 
Each  ounce  usually  holds  about  two  cubic  inches  of  carbon  dioxide. 
It  is  an  infusion  of  malt  fermented,  to  which  a  bitter  principle 
found  in  hops  is  added.  It  is  frequently  adulterated  with  salicylic 
acid  and  benzoic  acid  to  preserve  it.  In  excess  it  gives  rise  to  rheu- 
matism, gout,  and  bilious  attacks,  due  to  diminished  excretion  of 
waste-materials  from  the  economy.  Wines  contain  from  6  to  25  per 
cent,  of  alcohol.  Port  holds  10  per  cent,  and  sherry  16  to  25  per  cent. 
of  alcohol.  Besides,  the  aroma  is  due  to  ethers.  Champagnes  con- 
tain, in  addition,  10  per  cent,  of  sugar,  which  upsets  the  stomach. 
Wines  also  have  free  acids,  especially  tartaric,  which  also  disagree 
with  certain  stomachs. 

Spirits  contain  about  50  per  cent,  of  alcohol.  Alcohol  is  a 
nutrient  and  heat-generator.  One  gram  of  alcohol  produces  more  heat 
than  one  gram  of  proteid  or  carbohydrate.  Ordinarily  the  system  can 
oxidize  daily  about  one  and  one-half  ounces  of  alcohol.  When  alcohol 
is  oxidized  it  spares  the  fats  and  carbohydrates  and  probably  the  pro- 
teids.  It  is  well  known  that  the  continuous  drinking  of  alcohol 
makes  a  person  fat.  The  persistent  use  of  alcohol  also  increases 


ALIMENTARY  SUBSTANCES.  41 

the  dangers  of  infection  from  infectious  diseases.  In  fevers  its  use 
prevents  the  loss  of  fat  and  stimulates  the  secretion  of  gastric  juice. 
It  dilates  the  capillaries  of  the  skin  either  by  a  local  or  central  action. 
Its  habitual  use  gives  rise  to  chronic  gastritis  and  cirrhosis  of  the  liver. 
The  odor  of  spirits  in  the  breath  is  due  to  fusel-oil.  Alcohol  in  the 
blood  is  changed  into  carbonic  acid  and  water. 

Coffee. — Each  cup  of  coffee  contains  about  two  grains  of  caffeine. 
Coffee  also  contains  a  volatile  substance  called  coffeon,  which  resem- 
bles an  oil.  The  exhilaration  after  the  drinking  of  coffee  and  the 
increased  peristalsis  is  due  to  the  coffeon. 

Tea. — Tea  contains  caffeine  and  theophylline  and  about  7  per 
cent,  of  tannin.  Tea  induces  constipation  and  chronic  gastritis  when 
used  in  excess.  Neither  tea  nor  coffee  diminishes  metabolic  changes. 

Cocoa. — This  body  is  a  nutrient  because  it  contains  fat  (50  per 
cent.)  and  an  albuminous  substance.  It  contains  theobromine.  Caf- 
feine and  theobromine  belong  to  the  purin  group. 


CHAPTER  III. 

DIGE5TION. 

Anatomy  and  Structure  of  the  Mouth,  Pharynx,  and  (Esophagus, 
together  with  the  Digestive  Processes  Occurring  in  Them. 

DIGESTION  has  for  its  aim  the  separation  of  the  principles  of 
growth  and  repair  from  the  aliments  and  fitting  them  for  absorption 
into  the  circulation.  The  process  is  both  mechanical  and  chemical, 
accomplished  mainly  through  the  action  of  certain  soluble  ferments 
called  digestive  enzymes. 

Some  form  of  digestion  is  found  to  take  place  in  all  animal  organ- 
isms no  matter  how  low  we  proceed  in  the  zoological  scale.  It  is 
essential  to  every  one  of  them  that  they  be  able  to  take  from  their 
environments  those  elements  that  are  necessary  to  maintain  their 
economy  and  give  off  those  substances  that  are  no  longer  fit  for  use 
and  termed  waste-products,  for  only  by  this  exchange  of  the  elements 
outside  of  their  own  organisms  are  they  able  to  live,  grow,  and  produce 
others  of  their  kind. 

In  the  higher  grades  of  animal  life,  as  the  articulata  and  verte- 
brata,  the  number  of  organs  concerned  in  digestion  is  increased,  and, 
of  course,  in  direct  ratio  the  various  stages  and  acts  in  the  whole 
process  are  multiplied.  In  them  is  a  long  tube,  in  some  parts  much 
folded  on  itself;  in  and  along  the  outside  of  it  are  numerous  glands 
which  empty  their  products,  called  secretions,  into  the  long  tube ;  and 
at  the  beginning  of  which  there  is  an  apparatus  for  crushing  and 
grinding  the  solid  parts  of  the  food.  Intimately  connected  with  this 
apparatus  is  the  system  of  blood-  and  chyle-  vessels  for  absorbing  the 
digested  products  and  thus  allowing  them  to  circulate  through  the 
entire  body  and  come  into  contact  with  every  part  of  the  organism. 

In  the  vertebrata  there  are  modifications  and  forms  of  develop- 
ment dependent  upon  the  class,  and  even  in  mammalia  there  are  differ- 
ences as  the  animal  may  be  insectivorous,  carnivorous,  herbivorous,  or 
omnivorous. 

Man,  the  highest  of  the  mammalia,  is  the  real  and  intimate  study 
upon  which  all  our  physiological  researches  bear.  He  is  omnivorous, 
and  naturally  we  expect  to  find  his  digestive  apparatus  suited  to  dis- 
integrating and  dissolving  all  kinds  of  food. 

(42) 


DIGESTION. 


43 


In  him  the  digestive  apparatus  consists  of  a  long  tube,  called  the 
alimentary  canal,  about  thirty  feet  in  length,  with  its  accessories  of 
teeth  and  the  various  glands  which  empty  their  products  into  the  tube 
by  means  of  little  ducts. 

The  alimentary  canal  is  the  long  tube  beginning  with  the  mouth 
and  ending  with  the  anus,  composed  of  muscle  and  mucous  membrane, 
the  latter  lining  it  throughout  its  entire  length  and  giving  to  the 
interior  of  the  canal  its  characteristic  smoothness  and  redness.  In 
this  lining  membrane,  as  also  in  the  submucosa,  are  located  some  of 
the  glands  whose  secretions  aid  digestion. 

The  alimentary  canal  in  its  extent  of  about  thirty  feet  has 
received  various  names  for  its  several  parts.  They  are:  mouth, 
pharynx,  esophagus,  stomach,  small  and  large  intestines. 

The  mouth  is  the  oval  box,  situated  at  the  commencement  of  the 
canal,  in  which,  by  the  action  of  the  jaws  with  their  two  rows  of  teeth, 
the  hard  parts  of  the  food  are  masticated,  as  it  is  called.  While  the 
food  is  being  masticated  it  is  at  the  same  time  being  mixed  with  a 
watery  fluid,  the  saliva,  the  secretion  of  the  salivary  glands;  this  mix- 
ing of  food  and  saliva  has  been  termed  insalivation. 

In  the  pharynx  and  oesophagus  occurs  the  act  of  deglutition,  or 
swallowing  of  the  masticated  mouthful  in  the  form  of  a  large,  moist 
bolus.  It  is  by  the  contraction  of  the  muscles  in  these  parts  that  the 
food  is  quickly  passed  on  to  the  stomach.  The  course  of  the  tube 
beginning  with  the  mouth  and  ending  at  the  opening  of  the  stomach 
is  comparatively  straight  and  measures  about  fifteen  or  eighteen  inches 
in  length.  This  part  of  the  tube  is  found  in  the  head,  neck,  and 
thorax,  ending  just  below  the  transverse  muscular  wall  of  the  trunk, 
the  diaphragm. 

The  stomach  is  the  muscular  pouch  in  which  occurs  some  of  the 
chemical  changes  of  the  food,  converting  it  into  a  grayish-brown  soup- 
like  mass.  From  thence  it  passes  on  to  the  small  intestine,  where  the 
nutrient  materials  are  separated  from  the  waste-residue;  the  latter 
is  passed  on  to  the  large  intestine  to  be  later  expelled  from  the  body. 

The  stomach,  large  and  small  intestines  are  located  in  the  ab- 
domen and  pelvis,  differing  from  that  part  of  the  canal  above  the 
diaphragm  in  that  the  intestines  are  much  folded  and  convoluted  in 
their  course;  so  that  the  major  portion  of  the  entire  length  of  the 
canal  is  contained  here. 

In  the  mucous  membrane  and  submucosa  are  located  microscopical 
glands  whose  ducts  open  directly  upon  the  lining,  interior  surface. 
Outside  the  canal,  their  secretions  emptying  into  the  canal  by  small 


44  PHYSIOLOGY. 

ducts,  are  the  larger  glands:  salivary,  liver,  and  pancreas.  The  ducts 
of  the  salivary  glands  open  into  the  mouth ;  the  common  duct  of  the 
liver  and  pancreas  into  the  first  fold  of  the  small  intestine,  the  duo- 
denum. 

Although  digestion  in  its  entirety,  as  it  occurs  in  the  alimentary 
canal,  is  in  its  nature  very  complex,  yet  there  are  three  natural  divi- 
sions of  the  whole  process  based  upon  the  changes  as  they  occur  ( 1 )  in 
the  mouth  (including  the  pharynx  and  oesophagus),  (2)  in  the 
stomach,,  and  (3)  in  the  intestines. 

It  is  the  intention  to  consider  the  changes  and  alterations  of  the 
foodstuffs,  whether  mechanical  or  chemical,  in  each,  together  with  the 
anatomy  of  the  parts  of  each  division  and  the  structure  of  the  accessory 
glands,  with  their  secretions  and  the  functions  they  bear  to  the  com- 
pletion of  the  entire  work.  However,  the  fact  must  not  be  lost  sight 
of  that  these  divisions  are  only  arbitrary  and  for  convenience,  as  no 
real  line  can  be  drawn  at  the  various  stages,  since  all  parts,  structures, 
and  functions  work  in  harmony,  on  the  plan  of  division  of  labor: 
having  in  mind  one  common  end — the  dissolving  of  the  food  so  that 
it  can  become  a  part  of  the  circulation. 

PREHENSION. 

Before  the  processes  of  digestion  can  begin,  it  is  essential  that 
the  food  should  be  brought  to  and  placed  in  the  mouth,  the  beginning 
of  the  alimentary  canal,  for  only  in  some  of  the  infusoria  does  diges- 
tion of  the  food  take  place  outside  the  organism,  due  to  the  influence 
of  ferments  secreted  by  the  organism  to  be  nourished.  The  act  of 
bringing  the  food  to  the  mouth  has  been  termed  prehension. 

Nature  has  admirable  contrivances  for  this  act  wherever  we  look 
among  the  lower  animals.  The  monkey,  squirrel,  rat,  etc.,  usually 
make  use  of  their  anterior  extremities  for  grasping  and  bringing  to 
their  mouths  the  food,  while  they  sit  upon  their  haunches.  The 
horse  makes  use  of  his  teeth  and  lips;  indeed,  his  upper  lip  is  very 
movable,  long,  and  endowed  with  extreme  sensibility.  It  is  his  means 
of  gathering  together  his  grain  and  bringing  it  to  the  incisors  which 
cut  it  up,  then  to  be  passed  along  by  the  tongue  to  the  molars  for 
grinding.  In  the  cow  the  tongue,  in  the  cat  and  dog  the  teeth  and 
jaws,  are  the  main  organs  of  prehension.  The  frog,  by  protruding  his 
long,  thin  tongue,  the  surface  of  which  is  covered  with  a  viscid  mucus, 
catches  insects  as  they  fly. 

By  far  the  most  complicated  and  best  developed  prehensile  instru- 
ment in  animal  mechanics  is  that  employed  by  man — the  human 


DIGESTION. 

upper  limb.  The  extreme  perfection  of  all  its  part?,  and  particularly 
of  its  terminal  portion,  the  hand,  makes  it  admirably  fitted,  not  only 
for  the  prehension  of  food,  but  also  for  the  execution  of  all  the  various 
caprices  and  designs  of  the  human  will.  Thus  it  not  only  simply  raises 
the  food  to  the  mouth  (prehension),  but  also,  with  the  human  intelli- 
gence as  the  real  potent  factor,  aids  in  the  preparation  of  food  by 
means  of  fire  (cooking). 

Thus  we  learn  that  the  first  real  step  in  digestion  is  prehension : 
bringing  the  food  to  the  mouth. 

THE  MOUTH. 

The  space  included  between  the  lips  in  front,  the  pharynx  behind, 
and  the  cheeks  at  the  side  is  the  mouth.  Above  the  roof  of  the  mouth 
we  have  the  palate ;  below,  its  floor,  upon  which  rests  the  tongue.  The 
cavity  of  the  mouth,  excepting  the  teeth,  is  everywhere  invested  with 
a  highly  vascular  mucous  membrane,  with  an  investment  of  squamous 
epithelium.  Conical  papillae,  for  the  larger  part  minute  and  con- 
cealed beneath  the  epithelium,  are  found.  The  lips  are  separated  by 
the  oral  fissure.  They  are  composed  of  various  muscles  converging  to 
and  surrounding  the  oral  fissure.  The  cheeks  have  a  composition 
similar  to  the  lips,  and  their  principal  muscle  is  the  buccinator.  At 
their  back  part  they  include  the  ramus  of  the  jaw  and  its  muscles,  and 
usually  between  these  and  the  buccinator  muscle  is  a  mass  of  soft,  adi- 
pose tissue. 

Beneath  the  mucous  membrane  of  the  lips  and  cheeks  there  are  a 
number  of  small,  racemose  glands,  with  ducts  which  open  into  the 
mouth.  These  glands  are,  in  the  lips,  called  labial  and,  in  the  cheeks, 
buccal.  They  secrete  mucus.  « 

There  are  two  parts  to  the  palate :  a  hard  and  a  soft  palate.  The 
hard  palate  is  deeply  vaulted  and  lined  with  a  smooth  mucous  mem- 
brane, except  at  its  anterior  part,  where  it  is  roughened  by  transverse 
ridges.  The  soft  palate  is  a  doubling  of  the  mucous  membrane  in- 
closing a  fibromuscular  layer,  also  containing  racemose  glands.  It 
hangs  down  obliquely  from  the  hard  palate  between  the  mouth  and 
posterior  nasal  orifices.  It  is  a  freely  movable  partition.  The  uvula 
is  an  appendage  like  a  tongue  projecting  from  the  middle  of  the  soft 
palate,  and  consists  of  a  pair  of  muscles  inclosed  in  a  pouch  of  mucous 
membrane. 

Palate. — The  palate  has  two  crescentic  folds  of  mucous  mem- 
brane inclosing  muscular  fasciculi  and  diverging  from  the  base  of  the 
uvula,  on  each  side  of  the  palate  outward  and  downward,  one  to  the 


46  PHYSIOLOGY. 

side  of  the  tongue,  the  other  to  the  side  of  the  pharynx.  These  folds 
are  known  as  the  half-arches  of  the  palate.  The  one  in  front  is  known 
as  the  anterior  palatine  arch,  the  one  posterior  as  the  posterior  palatine 
arch. 

The  Fauces. — The  fauces  are  the  straits,  or  passages,  leading  from 
the  mouth  to  the  pharynx,  and  correspond  with  the  space  included 
between  the  half-arches  of  the  palate. 

Tongue. — The  tongue  is  composed  of  muscle  and  covered  with 
a  mucous  membrane.  It  is  composed  of  two  symmetrical  halves 
joined  in  the  middle  line.  By  the  freedom  of  its  movements  it  aids 
in  mastication  and  deglutition,  and  it  is  also  a  great  help  in  articula- 
tion, and  by  the  papillae  on  its  surface  forms  an  organ  of  taste.  The 
root,  or  base,  is  the  posterior  part,  where  it  is  attached  to  the  hyoid 
bone  and  inferior  maxilla.  The  body  is  the  great  bulk  of  the  organ. 
Its  tip  is  the  anterior  free  extremity.  On  the  anterior  two-thirds  of 
the  upper  surface  of  the  tongue  we  find  a  mucous  membrane  which  ad- 
heres most  intimately  to  the  muscles  beneath.  Its  surface  is  roughened 
by  the  presence  of  a  number  of  little  papillae.  On  the  surface  of  the 
tongue  there  are  many  mucous  glands. 

Papillae. — The  papillae  are  the  fungiform,  filiform,  and  circum- 
vallate.  These  are  more  minutely  described  in  the  section  on  the  sense 
of  taste. 

Nerves. — The  nerves  of  the  tongue  are  the  lingual  of  the  fifth 
pair,  the  glosso-pharyngeal,  and  the  hypoglossal. 

THE  TEETH. 

In  form,  structure,  and  number  the  teeth  vary  very  considerably 
among  different  animals,  which  is  markedly  shown  in  the  classes, 
carnivora  and  herbivora.  In  most  animals  the  teeth  are  worn  down 
by  use  and  eventually  decay.  The  exception  is  found  in  that  class 
of  animals  that  constantly  nibble;  their  incisors  are  peculiar  in  that 
there .  are  deposits  of  fresh  dentine  within  and  upon  the  pulp  and 
of  enamel  upon  the  anterior  surface,  thus  giving  a  continuous  growth. 
They  are  the  rodentia. 

Among  mammalia,  and  particularly  in  man,  the  teeth  are  devel- 
oped in.  two  sets:  (1)  the  first,  less  numerous  and  smaller  set,  called 
the  temporary,  or  milk,  teeth;  and  (2)  a  second  set,  larger  and  more 
numerous,  called  the  permanent  teeth. 

The  temporary,  or  milk,  teeth  are  usually  20  in  number,  10  in 
each  jaw.  In  each  jaw  there  are  4  incisors,  2  canines,  and  4  molars. 
When  the  milk  teeth  drop  out  they  are  followed  by  the  permanent 
teeth. 


DIGESTION. 


47 


The  permanent  teeth  are  32  in  number,  16  in  each  jaw,  consisting 
of  4  incisors,  2  canines,  4  bicuspids,  and  6  molars. 

There  are  three  distinct  parts  in  a  tooth :   crown,  root,  and  neck. 

The  crown,  or  body,  is  the  protruding  portion  of  the  tooth;  the 
portion  inserted  in  the  alveoli  of  the  jaws  is  the  root,  or  fang.  The 
slightly  constricted  part  enveloped  by  the  gum  is  the  neck.  The  fang 
is  firmly  fastened  to  the  sides  of  the  alveolus,  in  which  it  is  inserted  by 
fibrous  tissue,  which  is  continuous  with  the  periosteum  of  the  jaws. 
When  the  jaws  are  closed  the  under  incisors  are  inclosed  by  the  upper 
ones,  but  the  grinding  surface  of  the  molars  is  in  contact. 

Temporary  Teeth. — There  are  20  milk  teeth,  10  in  each  jaw,  or 
5  on  each  side  of  the  jaw;  that  is,  2  incisors,  1  canine,  and  2  molars. 
The  temporary  set  resembles  the  permanent  in  form  and  structure. 
The  teeth  are,  however,  fewer  in  number,  smaller  in  size,  and  charac- 
terized by  the  bulging  out  of  the  crown  close  to  the  neck,  making  the 
latter  very  sharply  defined. 

The  milk  teeth  die  off  and  so  give  room  for  the  second  and  more 
permanent  set.  They  die  partly  in  accordance  with  the  rule  of  epi- 
thelial tissues  and  drop  off,  since  all  such  tissues  are  expelled  after  their 
death;  then,  too,  the  jaws  grow  as  the  being  passes  from  infancy  to 
adult  life,  when  larger  and  more  numerous  teeth  must  replace  the 
smaller  ones,  so  as  not  to  impair  the  efficiency  necessary  to  masticate 
quantities  of  food  proportionate  to  the  demands  of  the  growing  body. 

Permanent  Teeth. — There  are  8  incisors,  and  they  form  the  4 
front  teeth  in  each  jaw,  and  are  named  incisors  because  they  divide 
the  food.  The  upper  incisors  are  the  larger. 

The  canine  teeth  are  4  in  number,  larger  than  the  incisors.  The 
upper  canines  are  usually  called  the  eye  teeth,  and  they  are  longer 
and  larger  than  the  canine  teeth  in  the  lower  jaw.  In  the  carnivorous 
animals,  like  the  dog,  the  canine  teeth  are  usually  large;  hence  the 
name  of  canine.  The  lower  canines  are  popularly  known  by  the  name 
of  stomach  teeth.  There  are  4  premolars,  or  bicuspids,  in  each  jaw. 
They  are  shorter  and  smaller  than  the  canines.  The  bicuspids  of  the 
upper  jaw  are  larger  than  those  of  the  lower  jaw.  The  function  of 
the  bicuspids  is  to  cut  and  grind  the  food.  The  molars  are  12  in 
number,  3  on  each  side  above  and  below.  Their  large  crown  and 
their  great  width  are  the  chief  distinguishing  characteristics.  The 
upper  molars  have  3  conical  fangs,  the  lower  ones  2.  The  last  molar 
is  the  wisdom  tooth,  so  called  because  it  appears  about  the  twentieth 
year,  when  the  individual  is  assumed  to  have  acquired  wisdom.  The 
molars  are  intended  for  the  grinding  of  food. 


48  PHYSIOLOGY. 

Structure  of  the  Teeth. — If  a  tooth  is  split  in  its  long  axis  the 
surface  exhibits,  besides  the  pulp-cavity,  three  different  kinds  of  mate- 
rials Dentine  forms  the  greater  part  of  the  yellowish-white  sub- 
stance; the  capping  of  the  crown  is  enamel;  and  the  translucent, 
thin  investment  on  the  fang  is  cement,  or  crusta  petrosa. 

The  main  bulk  of  the  tooth  is  composed  of  dentine,  giving  it 
shape  and  containing  the  pulp-cavity.  It  consists  of  about  28  parts 
of  organic  matter  and  72  of  earthy  material.  Dentine  resembles  bone 
both  physically  and  in  chemical  constitution.  When  subjected  to 
microscopical  examination  we  find  the  dentine  penetrated  throughout 
by  fine  tubes  called  dentinal  tubules.  The  inner  end  of  these  tubules 
open  into  the  pulp-cavity,  whence  they  radiate  in  every  part  of  the 
dentine  toward  the  surface  of  the  tooth.  They  have  a  direction  gen- 
erally parallel,  with  a  wavy,  undulating  course.  In  the  pathway 
toward  the  periphery  they  subdivide  into  several  parallel  branches 
which  anastomose  with  each  other.  The  average  diameter  of  the 
tubule  is  Y45o0  inch.  Near  the  end  of  the  tubule  the  arrangement  is  in 
globular  spaces  which  communicate  with  each  other  and  are  known 
as  the  interglobular  spaces  of  Purkinje. 

ENAMEL. — The  hardest  of  all  organized  substances  is  known  as 
enamel.  It  is  a  bluish-white  material  capping  the  crown  of  the  tooth. 
It  is  thickest  on  the  triturating  surface  of  the  tooth.  Chemically  it 
consists  of  3  parts  of  organic  matter  and  97  of  earthy  matters,  prin- 
cipally calcium  phosphate.  Under  the  microscope  the  enamel  appears 
in  the  form  of  hexagonal  columns  about  1/500o  inc^  in  diameter. 

THE  CEMENT,  OR  CRUSTA  PETROSA. — This  substance  covers  the 
fang  of  the  tooth,  gradually  becoming  thicker  toward  its  extremity. 
It  is  like  true  bone,  and  contains  lacunas  and  canaliculi.  Externally 
it  is  covered  by  dental  periosteum.  In  old  age  the  cement  grows 
thicker  and  may  close  up  the  entrance  to  the  pulp-cavity. 

THE  SALIVARY  GLANDS. 

The  parotid  gland  is  named  from  its  position  near  the  ear.  It 
is  the  largest  of  the  salivary  glands.  It  extends  upward  as  far  as  the 
zygoma,  as  far  down  as  the  angle  of  the  lower  jaw,  and  inwardly 
between  the  ramus  of  the  jaw  and  the  mastoid  process.  The  duct  of 
the  parotid,  called  Stenos,  has  the  diameter  of  a  crow-quill,  is  two 
inches  in  length,  and  runs  across  the  masseter  to  open  into  the  mouth 
opposite  the  second  molar  tooth. 

The  parotid  has  a  full  supply  of  blood-vessels,  which  run  through 
it.  The  nerves  of  the  parotid  are  the  auriculo-temporal  and  the 


DIGESTION.  49 

cervical  sympathetic.  In  the  dog  and  cat  the  parotid  derives  its 
nerve-supply  from  the  glosso-pharyngeal  through  the  small  petrosal 
and  the  otic  ganglion,  the  fibers  finally  running  in  a  branch  of  the 
auriculo-temporal. 

The  submaxillary  gland  is  separated  from  the  parotid  by  a  process 
of  the  deep  cervical  fascia.  It  is  beneath  the  mylohyoid  muscle,,  is 
below  the  curve  of  the  digastric  muscle,  and  on  the  outside  covered 
by  the  subcutaneous  cervical  muscle  and  skin.  It  is  about  one-third 
the  size  of  the  parotid,  and  its  duct  of  Wharton  is  about  two  inches 
in  length.  The  duct  opens  on  the  side  of  the  lingual  frasnum.  The 
blood-vessels  are  branches  of  the  facial  and  lingual.  The  nerves  are 
those  from  the  submaxillary  ganglion  and  through  this  from  the 
chorda  tympani.  The  sympathetic  also  supplies  this  gland. 

The  sublingual  gland  rests  on  the  floor  of  the  mouth  and  is  seen 
beneath  the  side  of  the  tongue  as  a  ridge.  It  has  a  half-dozen  ducts 
called  the  Bivinian,  which  open  on  the  ridge  which  marks  the  position 
of  the  gland  on  the  side  of  the  fraenum. 

STRUCTURE  OF  THE  SALIVARY  GLANDS. 

These  glands  are  of  the  compound  racemose  variety.  The  alveo- 
lus has  a  duct  ending  in  it.  The  alveoli  are  united  by  the  blood- 
vessels and  a  small  amount  of  loose  connective  tissue  with  lobules.  The 
alveoli  of  the  salivary  glands  are  divided  into  two  classes,  according  to 
the  kind  of  secretion,  one  kind  giving  a  secretion  containing  mucin, 
the  other  kind  secreting  a  more  watery  fluid  containing  a  large  amount 
of  serum-albumin;  hence  the  alveoli  are  mucous  or  serous.  The 
sublingual  chiefly  secretes  mucus,  the  parotid  chiefly  serum-albumin. 
The  submaxillary  secretes  both  kinds.  In  most  of  the  alveoli  of  the 
glands  there  are  found  cells  of  a  kind  differing  from  the  mucin-cells, 
as  in  the  submaxillary  of  the  cat,  where  they  form  an  almost  complete 
outer  layer  next  to  the  basement  membrane,  inclose  the  mucin-cells, 
and  are  called  "marginal  cells."  In  the  dog's  submaxillary  they  are 
only  seen  as  semilunar  masses  known  as  the  half-moons  of  Gianuzzi. 
The  lymphatics  lie  closer  to  the  alveoli  than  the  capillary  network  of 
blood-vessels.  The  lymphatics  begin  in  the  form  of  lacunae  between 
and  around  the  alveoli.  The  nerves  pierce  the  basement  membrane 
and  arborize  between  and  around  the  cells  of  the  alveoli. 

PHARYNX. 

The  pharynx  is  a  funnel-like  cavity  running  from  the  under  sur- 
face of  the  skull  down  to  the  level  of  the  fifth  cervical  vertebra,  where 


50  PHYSIOLOGY. 

it  ends  in  the  oesophagus.  There  are  7  openings  communicating  with 
it:  the  2  posterior  nares,  the  2  Eustachian  tubes,  the  mouth,  the 
larynx,  and  the  oesophagus.  The  walls  of  the  pharynx  are  musculo- 
membranous.  The  interior  is  lined  with  a  soft,  red,  mucous  mem- 
brane containing  many  glands.  Squamous  cells  are  the  chief  variety 
of  epithelium  lining  the  mucous  membrane.  Next  is  a  fibrous  coat, 
then  a  muscular  coat,  and  outside  of  this  a  fibrous  investment  which 
attaches  it  to  the  skull.  The  muscular  coat  includes  the  superior, 
middle,  and  inferior  constrictors  of  the  pharynx,  which  are  concerned 
in  deglutition.  Lymphoid  tissue  is  very  abundant  at  the  upper  back 
part  of  the  pharynx,  and  a  number  of  lymph-follicles  lie  between  the 
orifices  of  the  Eustachian  tubes,  forming  the  pharyngeal  tonsil. 

OESOPHAGUS. 

This  tube  extends  from  the  fifth  cervical  down  to  the  ninth  dorsal 
vertebra.  It  is  about  nine  inches  long  and  less  than  an  inch  in 
diameter.  It  is  narrowest  at  its  commencement  and  gradually  en- 
larges. It  has  three  coats:  from  the  outside,  muscular;  a  middle 
coat,  fibrous;  and  an  internal,  or  mucous,  coat.  The  muscular  coat 
has  a  layer  of  longitudinal  fibers  and  a  circular  layer,  the  upper  end 
of  the  oesophagus  has  striated  fibers,  while  the  lower  half  has  plain, 
unstriped  fibers.  The  mucous  coat  is  paler  than  that  of  the  pharynx 
and  mouth.  In  ordinary  circumstances  the  mucous  membrane  is  in 
longitudinal  folds.  It  contains  minute  papilla?  and  a  squamous  epi- 
thelium. The  nerves  of  the  oesophagus  are  the  vagus  and  the  sym- 
pathetic. 

THE  MECHANICAL  PROCESSES  OF  DIGESTION  OCCURRING 
IN  THE  MOUTH,   PHARYNX,  AND  (ESOPHAGUS. 

MASTICATION. 

This  -is  a  voluntary  act  whereby  the  food  is  comminuted  by  the 
teeth,  jaws,  and  muscles  concerned  in  this  act,  aided  by  the  tongue, 
palate,  cheeks,  and  lips.  The  bulk  of  the  work  is  accomplished  by 
the  biting  and  grinding  movements  of  the  lower  teeth  against  the 
upper  ones. 

From  the  manner  of  its  articulation  with  the  skull  the  lower  jaw 
is  capable  of  performing  three  primary  movements,  together  with 
combinations  of  these  same,  viz. :  up  and  down,  side  to  side,  with 
projection  and  retraction.  The  muscles  concerned  in  producing  these 
movements  are  the  masseter,  temporal,  and  internal  pterygoids,  which 


DIGESTION.  51 

raise  the  lower  jaw;  the  inferior  maxillary  division  of  the  fifth  nerve 
innervates  them.  The  depression  of  the  jaw  is  accomplished  mainly 
through  the  action  of  the  digastric,  aided  considerably  by  gravity. 
The  side-to-side,,  or  lateral,  movements  are  due  to  the  separate  action 
of  the  external  pterygoids.  Their  united  contraction  gives  projection 
of  the  lower  mandible,  to  be  retracted  by  a  part  of  the  temporal  muscle. 
The  innervation  of  the  pterygoids  is  also  by  the  inferior  division  of 
the  fifth. 

Mastication  is  particularly  important  when  solid  and  fibrous  foods 
are  eaten,  to  prepare  them  by  comminution  for  the  fermentative  action 
of  the  various  digestive  fluids.  When  improperly  performed  repeat- 
edly a  severe  form  of  dyspepsia  ensues. 

During  mastication  there  is  performed  a  separate  and  distinct  act, 
insalivation,  or  the  mixing  of  the  food  with  saliva.  By  means  of  it, 
the  dry,  hard  portions  of  food  are  moistened  and  softened  better  to  fit 
them  for  swallowing;  at  the  same  time  the  mucous  membrane  is 
lubricated  to  allow  free  movement  of  the  food  over  its  surface  and 
the  surf  aces -of  the  teeth  are  freed  from  accumulations  of  food  during 
mastication  which  otherwise  would  collect  and  impede  its  progress.  A 
fever  patient  attempting  to  swallow  a  dry  cracker  affords  ample  illus- 
tration of  the  mechanical  value  of  the  saliva  during  mastication. 

DEGLUTITION. 

The  swallowing  of  the  food,  which  has  been  named  the  act  of 
deglutition,  is  performed  by  the  aid  of  the  tongue,  fauces,  pharynx, 
and  the  oesophagus  or  gullet.  For  the  purpose  of  description  only, 
since  the  process  in  reality  admits  of  no  lines  of  distinction,  this  act 
is  usually  said  to  comprise  three  stages:  first,  that  in  which  the  food 
is  forced  backward  from  the  mouth,  through  the  fauces,  into  the 
pharynx.  This  act  is  voluntary,  though  usually  performed  uncon- 
sciously, being  ascribed  to  the  movements  of  the  tongue  itself.  The 
second  stage  is  that  in  which  the  bolus  is  made  to  travel  along  the 
middle  and  lower  part  of  the  pharynx  to  the  oesophagus.  This  second 
act  is  more  complicated  and  requires  quicker  movements,  because  the 
nasal  and  laryngeal  orifices  are  open,  but  past  which  the  food  must 
go  without  entering.  The  main  motive  power  for  this  performance  is 
gained  by  the  contractions  of  the  three  constrictors,  aided  by  the 
synchronous  action  of  other  muscles,  whose  duty  is  to  occlude  tem- 
porarily the  nasal  and  laryngeal  openings.  The  opening  into  the 
nasal  cavity  is  closed  by  the  elevation  of  the  soft  palate,  uvula,  and 
the  contraction  of  the  posterior  pillars  of  the  fauces.  Just  above  the 


52  PHYSIOLOGY. 

laryngeal  opening  and  at  the  base  of  the  tongue  is  a  small,  leaf-shaped 
piece  of  cartilage,  the  epiglottis.  It  was  formerly  believed  that  the 
laryngeal  orifice  was  guarded  during  deglutition  by  the  retraction  of 
the  tongue  pressing  down  the  epiglottis  to  fit  it  firmly.  But,  as  re- 
moval of  the  epiglottis  did  not  interfere  with  normal  swallowing,  it 
was  learned  that  the  real  safeguard  was  the  contraction  of  the  aryteno- 
epiglottic  folds.  The  third  stage  is  that  in  which  the  bolus  descends 
along  the  oesophagus  to  enter  the  stomach.  This  stage  is  performed 
by  the  intrinsic  contractions  of  the  muscular  fibers  of  the  oesophagus- 
walls.  As  is  known,  its  muscular  fibers  are  arranged  in  two  layers : 
one  circular,  the  other  longitudinal.  The  upper  third  is  composed  of 
striated  muscle-fibers,  the  lower  two-thirds  of  the  plain,  or  unstriped, 
variety.  Accordingly  in  the  upper  third  the  movement  of  the  bolus 
is  more  rapid  than  in  the  lower  two-thirds.  The  movement  through 
the  oasophagus  is  that  known  as  peristaltic,  or  vermicular.  The  sec- 
ond and  third  stages  of  deglutition  are  involuntary.  When  the 
death-rattle  occurs  it  is  caused  by  the  pharynx  not  contracting  around 
the  bolus. 

Swallowing   of   Fluids. 

From  what  has  been  said  previously  it  will  be  readily  perceived 
that  the  act  of  deglutition  of  both  liquids  and  solids  is  a  muscular  act, 
and  not,  therefore,  dependent  upon  gravity.  Thus,  horses  and  many 
other  animals  drink  with  their  heads  low,  so  that  the  fluid  must  needs 
be  forced  up  an  inclined  plane  to  reach  their  stomachs.  Sometimes 
jugglers,  while  standing  upon  their  heads,  perform  the  feat  of 
drinking. 

The  deglutition  of  boli  or  food  was,  for  convenience,  divided 
into  three  stages,  but  so  quickly  is  the  passage  of  liquids  accomplished 
that  physiologists  are  able  to  recognize  but  one  movement  when  they 
are  swallowed.  We  are  indebted  to  the  experiments  and  observations 
of  Kronecker  and  Meltzer  for  an  explanation  of  this  process ;  accord- 
ing to  them,  there  is  an  action  resembling,  in  the  main,  that  of  a  force- 
pump,  whereby  the  mass  of  liquid  is  propelled  with  extreme  rapidity 
through  the  pharynx  and  oesophagus. 

It  is  by  the  contraction  of  the  two  mylo-hyoids  that  the  liquid 
is  put  under  high  pressure  and  shot  along  in  the  direction  of  least 
resistance:  through  the  pharynx  and  oesophagus.  This  pair  of  mus- 
cles is  greatly  aided  by  the  simultaneous  action  of  the  two  hyoglossi 
muscles.  These  two  pairs  of  muscles,  by  acting  in  unison,  form  a 
sort  of  diaphragm  to  push  the  root  of  the  tongue  backward  and  down- 
ward, at  the  same  time  performing  a  force-pump  action  upon  the 


DIGESTION.  53 

liquid  to  be  swallowed.  So  quickly  is  the  passage  of  the  liquid  accom- 
plished that  the  pharyngeal  and  oesophageal  muscles  have  not  time  to 
contract  about  the  mass  of  liquid;  in  fact,  they  are  inhibited  during 
the  passage  of  liquids  through  their  respective  channels.  After  the 
liquids  arrive  in  the  stomach  the  act  of  deglutition  ensues  for  the  pur- 
pose of  removing  the  liquids  adhering  to  the  walls  of  the  oesophagus. 

This  statement  is  substantiated  very  strikingly  in  cases  of  poison- 
ing by  carbolic  acid  and  other  corrosive  substances.  The  mouth  and 
tongue,  from  longer  contact,  are  always  burned,  while  the  pharynx 
and  oesophagus  may  escape  altogether,  or,  at  most,  are  but  slightly 
burned.  The  escape  of  the  latter  is  due  to  the  rapid  transit  of  the  cor- 
rosive substance  through  them.  However,  the  cardiac  entrance  of  the 
stomach  is  always  very  much  corroded  before  the  sphincter  relaxes 
for  admission  into  the  stomach. 

When  the  ingested  food  has  been  thoroughly  insalivated  or  is 
semisolid,  there  begins  to  be  a  departure  from  the  three-stage  act 
toward  the  force-pump  action  of  liquids.  When  the  food  is  very 
much  liquefied  the  latter  action  is  very  prominent;  so  that  any  fixed 
line  for  the  swallowing  of  food  or  liquids  does  not  exist. 

Nervous  Control  of   Deglutition. 

Deglutition  is  a  reflex  act.  Every  reflex  act  requires  an  afferent 
set  of  sensory  nerves,  a  reflex  center,  and  an  efferent  set  of  motor 
nerves,  that  of  swallowing  no  less  so  than  any  other.  The  sensory 
nerves  have  their  terminations  in  the  mucous  membrane  of  the 
pharynx  and  oesophagus,  including  branches  of  the  glosso-pharyngeal 
to  the  tongue  and  pharynx,  branches  of  the  fifth  to  the  soft  palate, 
and  the  superior  laryngeal  branch  of  the  vagus  innervating  the  glottis 
and  epiglottis.  The  reflex  center  lies  somewhere  forward  in  the 
medulla.  The  efferent  nerves  are :  Branches  of  the  fifth,  which  sup- 
ply the  digastric,  mylo-hyoid,  and  muscles  of  mastication;  the  facial. 
which  supplies  the  levator  palati;  the  glosso-pharyngeal  supplies  the 
muscles  of  the  pharynx.  Stimulation  of  the  central  end  of  the  superior 
laryngeal  calls  out  an  act  of  deglutition.  Stimulation  of  the  central 
end  of  the  glosso-pharyngeal  arrests  it.  The  inferior  laryngeal  branch 
of  the  vagus  innervates  the  muscles  of  the  larynx,  while  the  hypo- 
glossal  is  distributed  to  the  intrinsic  muscles  of  the  tongue.  Division 
of  the  two  vagi  is  followed  by  paralysis  of  both  oesophagus  and 
stomach,  with  a  very  firm  contraction  of  the  circular  band  of  fibers 
guarding  the  cardiac  orifice.  Therefore  these  nerves  send  motor  fibers 
to  the  oesophagus  and  stomach,  but  inhibitory  ones  to  the  cardiac 


54  PHYSIOLOGY. 

sphincter.  So  firm  is  the  tetanic  contraction  of  the  sphincter  that  if 
food  is  swallowed  after  division  of  the  vagi  it  accumulates  within 
the  oesophagus,  no  part  of  it  passing  into  the  stomach. 

The  act  of  swallowing  inhibits  the  vagus  center,  for  a  single  act 
of  deglutition  increases  the  pulse-rate.  This  influence  upon  the  heart- 
beat is  dependent  upon  neither  the  amount,  character,  nor  temperature 
of  the  bolus  swallowed.  It  is  influenced  only  by  the  reflex  act  and 
the  summation  of  other  acts.  It  also  has  an  inhibitory  influence  upon 
the  respiration.  This  is  very  evident  during  rapid  drinking  in  an 
animal  with  a  tracheotomy  tube.  For  increasing  the  activity  of  the 
heart's  action  a  tablespoonful  of  water  taken  in  a  large  number  of 
swallows  is  more  beneficial  than  a  glass  of  wine  taken  in  one  swallow. 

THE  CHEMICAL  CHANGES  OCCURRING  IN  THE  MOUTH 
DURING  DIGESTION. 

As  before  stated,  the  chief  aim  of  digestion  in  the  animal  economy 
is  the  reduction  of  the  alimentary  substances  into  a  soluble  and  ab- 
sorbable  condition  before  they  can  pass  through  the  various  animal 
membranes  and  so  become  components  of  the  tissues  and  blood  of  the 
body.  No  matter  how  soft,  through  the  influence  of  insalivation,  or 
finely  divided  and  triturated  by  reason  of  mastication,  the  food  may 
be,  it  cannot  become  a  constituent  of  the  body  until  it  has  been  acted 
upon  chemically  and  dissolved  by  the  various  ferments  present  in  the 
different  digestive  fluids. 

When  food  enters  the  mouth,  the  commencement  of  the  digestive 
tract,  the  first  digestive  fluid  that  it  comes  in  contact  with  is  the  saliva. 
Besides  its  mechanical  functions  of  moistening  and  softening  the  food 
to  render  easier  the  task  of  swallowing  it  in  the  form  of  boli,  it  per- 
forms other  duties  of  a  chemical  nature. 

First,  by  reason  of  its  watery  base,  it  has  the  power  to  dissolve 
saline  substances,  the  organic  acids,  alcohols,  sugars,  and  a  few  other 
substances  soluble  in  water. 

Secondly,  it  has  the  power  to  transform  certain  materials,  as 
starches,  into  maltose,  a  form  of  sugar.  The  starch  must  have  its 
cellulose  coat  dissolved  by  boiling,  however,  for  the  ferment  in  saliva 
will  not  act  readily  upon  cellulose.  The  active,  transforming  prin- 
ciple in  saliva  is  an  unorganized  ferment,  or  enzyme,  to  which  the 
name  ptyalin  has  been  given.  The  conversion  of  starch  into  sugar  by 
it  is  known  as  the  amylolytic  action  of  saliva.  Its  action  is  by  more 
contact,  for  no  appreciable  change  in  quantity  or  character  is  noted  in 


DIGESTION.  :,;, 

it  after  its  functions  are  performed,  and  so  active  is  it  that  it  is  able 
to  convert  two  thousand  times  its  own  weight  of  starch  into  sugar. 

Ferments  do  not  initiate  a  chemical  action,  but  alter  the  velocity 
of  reaction,  which  occurs  in  their  absence,  only  then  much  more  slowly 
or  much  more  quickly. 

Saliva,  as  it  appears  in  the  mouth,  is  a  thick,  glairy,  generally 
frothy  and  turbid  fluid.  It  is  a  mixed  fluid,  its  secretions  being  de- 
rived from  the  parotid,  submaxillary,  and  sublingual  salivary  glands, 
and  contains  mucin  procured  from  the  labial,  lingual,  and  buccal 
glands.  Then,  too,  it  contains  some  debris  of  food,  bacteria,  and  the 
so-called  salivary  corpuscles.  Its  thick,  ropy  nature  is  due  to  the  pres- 
ence of  the  mucin  in  it.  Normal  saliva  is  alkaline  in  reaction,  al- 
though in  some  forms  of  dyspepsia  it  becomes  somewhat  acid.  The 
specific  gravity  ranges  from  1.002  to  1.006. 

The  amylolytic  action  of  saliva  is  sensitive  to  changes  of  tem- 
perature, a  low  temperature  either  retarding  its  action  or  stopping  it- 
altogether,  while  increased  temperature  causes  greater  activity  until 
40°  C.  is  reached,  which  is  considered  the  optimum  point.  Above 
that  mark  the  heat  becomes  injurious. 

During  the  proper  mastication  and  insalivation  of  a  mouthful 
of  food  there  occurs  to  the  starches  present  a  splitting  up  into  dextrin 
and  maltose;  the  dextrin  is  later  converted  into  maltose  also.  This 
occurs  more  quickly  with  erythrodextrin,  which  gives  a  characteristic 
red  color  with  iodine,  than  with  achroodextrin,  which  gives  no  color 
with  iodine. 

The  amylolytic  action  of  saliva  is  best  favored  by  a  neutral 
medium,  although  it  can  take  place  when  the  environment  is  slightly 
alkaline  or  acid.  The  slightest  quantity  of  free  acid  in  excess  stops 
its  action  at  once.  Its  normal  condition  in  the  mouth  is  slightly 
alkaline  or  neutral.  In  these  media  the  splitting-up  process  takes 
place  quickly ;  but,  since  the  food  is  usually  'held  in  the  mouth  for  so 
short  a  time,  all  the  starches  cannot  be  transformed  during  the  period 
of  mastication.  As  the  gastric  juice  contains  free  hydrochloric  acid, 
it  has  been  generally  thought  that  immediately  the  bolus  of  food  comes 
in  contact  with  the  gastric  juice  the  ptyalin  of  the  saliva  is  killed  and 
its  amylolytic  action  stopped.  Eecent  researches  have  proved  that  the 
transforming  continues  in  the  stomach  for  some  time  after  its  entry, 
the  time  ranging  from  fifteen  to  thirty  minutes.  That  is,  until  (a) 
the  alkalinity  of  the  saliva  has  been  neutralized  and  (b)  until  a  trace 
of  free  hydrochloric  acid  remains  in  excess.  According  to  Veldin,  free 
hydrochloric  acid  does  not  occur  in  the  stomach  until  about  three- 
fourths  of  an  hour  after  a  meal. 


56  PHYSIOLOGY. 

The  action  of  saliva  upon  starch  is  very  readily  seen  by  test-tube 
experimentation.  In  a  tube  is  placed  a  quantity  of  boiled  starch, 
which  is  viscid  and  gelatinous  in  nature  and  rather  turbid  in  appear- 
ance. That  it  is  true  starch  may  be  shown  by  the  iodine  test,  a  blue 
color  resulting.  With  the  starch  in  the  tube  is  mixed  a  quantity  of 
saliva.  Soon  there  is  a  marked  change :  the  solution  becomes  more 
watery  and  thinner  and  the  turbidity  disappears.  On  boiling  a  por- 
tion of  this  transparent  solution  with  Fehling's  solution  a  cuprous 
oxide  is  precipitated,  showing  the  presence  of  sugar  in  the  form  of 
dextrose  or  maltose.  The  saliva  also  contains  traces  of  an  inorganic 
substance,  potassium  sulphocyanide.  Tincture  of  iron  stains  it  red. 

In  the  resting  serous  gland  when  stained  with  carmin  it  is  found 
that  the  cells  are  pale,  with  but  little  color,  and  containing  a  few 
minute  granules.  The  nucleus  is  small  sized,  without  a  nucleolus ;  in 
shape,  irregular,  and  red  stained.  The  shrinking  of  the  nucleus  is 
well  marked.  In  the  active  stage  the  cells  are  smaller,  the  nuclei  are 
round,  with  sharp  walls  containing  nucleoli.  The  contents  of  the  cell 
are  turbid,  due  to  the  lessening  of  the  clear  substance  and  an  increase 
of  granules.  The  carmin  stains  the  cells  more  profoundly. 

The  salivary  glands  are  greatly  influenced  by  nervous  activity. 
The  submaxillary  is  supplied  by  the  chorda  tympani,  which  contains 
two  kinds  of  fibers:  the  secretory  and  the  vasodilator.  If  you  give 
atropine  you  can  paralyze  the  endings  of  the  secretory  fibers  while 
the  vasodilator  still  continue  their  activity.  Injection  of  sodium 
bicarbonate  into  the  duct  of  Wharton  arrests  the  action  of  the  secretory 
fibers  and  leaves  intact  the  vasodilators.  Pilocarpine  and  muscarine 
increase  the  flow  of  saliva  by  stimulating  the  endings  of  the  chorda 
tympani  and  will  remove  the  paralysis  of  them  by  atropine.  Opium 
makes  the  mouth  dry  by  acting  on  the  center  of  salivation.  The 
salivation  by  mercury  is  due  to  excessive  metabolism  of  the  gland-cells 
themselves.  When  the  chorda  is  stimulated  by  electricity  the  pressure 
in  the  excretory  duct  is  greater  than  the  blood-pressure  of  the  animal. 
During  this  stimulation  the  temperature  is  elevated.  When  the 
chorda  tympani  is  stimulated  the  blood-vessels  of  the  gland  dilate  and 
the  veins  are  red  and  pulsate  because  the  arterial  blood  rushes  rapidly 
through  them.  The  antagonistic  nerve  which  slows  the  secretion  of 
saliva,  both  in  the  submaxillary  and  parotid  gland,  is  the  cervical 
sympathetic.  At  the  same  time,  owing  to  its  vasoconstrictors,  the 
blood-vessels  are  contracted.  Hence  in  the  submaxillary  we  have  as 
a  secretory  nerve  the  chorda  tympani;  in  the  parotid  the  auriculo- 
temporal.  The  nerve  playing  against  them  both  is  the  cervical  sympa- 


DIGESTION.  57 

thetic.  The  reflex  center  for  the  salivary  secretion  is  situated  in  the 
medulla  oblongata,  near  the  origin  of  the  ninth  and  seventh  cranial 
nerves.  The  afferent  nerves  are  the  nerves  of  taste,  the  chorda 
tympani  and  the  glosso-pharyngeal  and  sensory  branches  of  the  tri- 
geminus;  the  efferent  nerves  are  the  auriculo-temporal  and  chorda 
tympani. 

GASTRIC  DIGESTION  (DIGESTION  IN  THE  STOMACH). 

The  stomach  is  the  principal  organ  of  digestion.  As  we  know, 
digestion  has  for  its  aim  the  rendition  of  the  organic  and  inorganic 
substances  ingested  from  the  external  world  into  such  a  condition 
that  they  can  readily  mix  with  the  blood  and  so  be  introduced  into  the 
living  tissues  of  the  body.  For  no  animal  can  exist  which  does  not 
receive  materials  for  its  support  from  the  environing  media.  To 
accomplish  this  aim  both  chemical  and  mechanical  changes  are  closely 
interwoven.  In  the  stomach,  as  one  of  the  principal  organs,  is  per- 
formed a  large  and  important  share  of  the  whole  digestive  process ;  as 
it  were,  it  is  one  of  the  large  departments  of  a  mechanical  and  chem- 
ical laboratory  or  establishment  in  which  every  department  is  working 
toward  a  definite  end :  the  digestion  of  the  food.  Unlike  the  amylo- 
lytic  changes  of  the  saliva  which  best  occur  in  an  alkaline  solution, 
stomachic  digestion  is  an  acid  digestion. 

The  stomach  is  the  first  organ  into  which  the  food  passes  as  it 
leaves  the  oesophagus.  It  is  the  most  enlarged  or  dilated  portion  of 
the  entire  alimentary  canal,  being  located  in  the  left  hypochondriac, 
epigastric,  and  right  hypochondriac  regions.  It  is  a  large  muscular 
pouch,  and  extends  from  the  oesophagus  to  the  small  intestine.  The 
greater  extremity  of  the  stomach  is  to  the  left  and  communicates  with 
the  oesophagus  by  the  cardiac  orifice.  The  pyloric  end  is  the  lesser 
extremity,  and  at  the  right  communicates  with  the  small  intestine  by 
the  pyloric  orifice. 

The  fundus  is  the  greater  extremity  of  the  stomach,  and  projects 
several  inches  to  the  left  of  the  oesophagus.  The  lesser  extremity  for 
about  two  inches  of  its  length  is  slightly  constricted,  and  is  called  the 
pyloric  antrum.  The  pyloric  orifice  is  the  entrance  to  the  duodenum, 
and  is  about  a  half-inch  in  diameter.  It  contains  the  pyloric 
sphincter,  or  valve. 

STRUCTURE  OF  THE  STOMACH. 

The  stomach  has  four  coats :  from  the  outside,  serous,  muscular, 
fibrous,  and  mucous.  The  serous  coat  is  derived  from  the  peritoneum. 


58  PHYSIOLOGY. 

The  muscular  coat  contains  three  layers  of  unstriped  muscular 
fibers.  The  layer  of  longitudinal  fibers  is  continuous  with  that  of 
the  oesophagus,  from  which  it  radiates  over  the  stomach. 

The  middle  layer  is  composed  of  circular  fibers.  These  circular 
fibers  gradually  accumulate  toward  the  pyloric  extremity  and  form  a 
thick  band  known  as  the  pyloric  sphincter.  The  internal  layer  con- 
sists of  oblique  fibers.  The  submucous  coat  is  made  up  of  areolar 
tissue  and  forms  an  extensible  layer  upon  which  the  strength  of  the 
stomach  mainly  depends.  The  mucous  membrane  of  the  stomach  is 
soft  to  the  touch  and  of  a  pale-pinkish  color.  Under  excitement  it 
becomes  reddened.  During  digestion  and  when  inflamed  it  has  a 
deep-red  hue.  It  is  thin  at  the  fundus  and  gradually  thickens  toward 
the  pyloric  extremity.  In  this  place  it  ordinarily  is  in  a  state  of 
wrinkles  or  rugse,  which  are  longitudinal  in  great  part.  At  the  pyloric 
orifice  a  thick  circular  fold  acts  as  a  part  of  a  valve  called  the 
pyloric  valve. 

Structure  of  Mucous  Membrane. 

Upon  an  examination  with  a  feeble  magnifying  power  there  is 
found  on  the  mucous  membrane  a  great  number  of  depressions  about 
1/200  inch  in  diameter,  which  are  the  openings  of  the  glands  of  the 
stomach.  The  mucous  membrane  is  lined  with  a  columnar  epithelium. 
The  tubular  glands  of  the  stomach  are  placed  side  by  side  and  number 
several  millions.  These  glands  have  a  basement  membrane,  which 
separates  the  glands  from  one  another  and  in  which  the  capillaries 
spread  a  fine  network  over  the  tubules.  They  have  also  a  blind  end. 
They  are  two  kinds  of  gastric  glands:  the  cardiac  and  the  pyloric. 
The  pyloric  glands  have  at  their  mouth  an  epithelium  which  is  a  con- 
tinuation of  the  columnar  epithelium  of  the  stomach.  In  the  tubules 
the  epithelium  is  shorter  and  more  cubical  and  granular.  In  the 
fundus  glands  and  cardiac  glands  the  epithelium  is  composed  of  short 
columnar  cells,  and  these  cells  have  coarser  granules  than  the  pyloric 
glands.  These  are  the  central,  or  adelomorphous,  cells.  Between 
these  cells  and  the  basement  membrane  there  are  other  cells,  oval  in 
shape,  with  distinct  oval  granular  nuclei,  called  the  parietal,  or  delo- 
morphous  or  oxyntic,  cells. 

The  blood-vessels  of  the  stomach  are  derived  from  the  three  divi- 
sions of  the  cceliac  axis.  The  veins  are  the  tributaries  of  the  portal 
vein,  and  contain  numerous  valves.  The  nerves  are  the  vagus  and 
sympathetic.  Numerous  small  gangliated  plexuses  are  found:  those 
of  Meissner  in  the  submucous  coat,  like  those  in  the  intestine;  and 
Auerbach's,  between  the  muscular  fibers,  also  found  in  the  intestine. 


DIGESTION.  59 

Movements  of  the  Stomach. 

Dr.  Beaumont,  upon  a  human  stomach,  ascertained  that  a  very 
feeble  peristaltic  contraction  begins  at  the  cardiac  orifice,  to  proceed 
toward  the  pylorus  by  way  of  the  greater  curvature,  for  only  along 
it  is  any  movement  apparent.  The  wave  grows  stronger  until  the 
special  band  separating  the  antrum  from  the  fundus  is  reached,  when 
the  contraction  becomes  so  strong  that  the  stomach  presents  an  hour- 
glass appearance.  Immediately  the  entire  antrum  contracts  at  one 
time  as  a  unit ;  so  that,  if  the  contents  are  properly  acted  upon  by  the 
gastric  secretion,  they  are  propelled  by  this  movement  through  the 
pylorus  into  the  duodenum.  If,  as  very  frequently  happens,  the  semi- 
liquid  mass  contains  solid  portions  of  too  great  bulk  to  pass  through 
the  opening,  a  muscular  wave  is  set  up  in  the  opposite  direction.  The 
direct  result  of  this  is  to  force  into  the  fundus  through  the  now  relax- 
ing temporary  sphincter  the  food-mass,  from  where  the  whole  process 
is  begun  again.  These  movements  occur  with  a  certain  degree  of 
regularity  and  rhythm,  once  in  about  every  two  or  three  minutes ;  the 
time  and  regularity  are,  however,  much  influenced  by  the  quantity 
and  quality  of  the  food  ingested.  As  a  result  of  these  combined 
movements,  not  only  is  the  chymified  food  propelled  into  the  duo- 
denum, but  there  are  set  up  regular  currents  among  the  contents. 

Dr.  Cannon  has  studied  the  movements  of  the  stomach  in  cats 
by  means  of  the  Koentgen  rays.  He  states  that  the  stomach  consists 
of  two  physiologically  distinct  parts :  the  pyloric  part  and  the  fundus. 
Over  the  pyloric  part  while  food  is  present  constriction  waves  are  seen 
continually  coursing  toward  the  pylorus.  The  fundus  is  an  active 
reservoir  for  the  food,  and  squeezes  out  its  contents  gradually  into  the 
pyloric  part.  The  stomach  is  emptied  by  the  formation  between  the 
fundus  and  the  antrum  of  a  tube  along  which  the  constrictions  pass. 
The-  contents  of  the  fundus  are  pressed  into  the  tube  and  the  tube 
and  antrum  slowly  cleared  of  food  by  the  waves  of  constriction.  The 
constriction  waves  have  three  functions :  the  mixing,  trituration,  and 
expulsion  of  the  food.  The  stomach  movements  are  inhibited  when 
the  cat  shows  anxiety,  rage,  or  distress.  Cannon  has  observed  in  cats 
that  carbohydrate  food  appeared  in  the  intestine  in  ten  minutes, 
while  proteid  did  not  leave  for  an  hour.  Proteids  also  remained  in 
the  stomach  twice  as  long  as  the  fats. 

CLOSURE  OF  THE  PYLORUS. 

Each  time  the  acid  chyme  escapes  it  sets  up  a  roflox  act  which 
temporarily  occludes  the  pyloric  orifice  and  at  the  same  time  inhibits 


GO  PHYSIOLOGY. 

the  propulsive  movements  of  the  organ.  The  acid  mass  of  chyme 
escaping  the  pylorus  excites  an  increased  secretion  of  pancreatic  juice 
and  the  acid  is  gradually  neutralized.  When  this  is  accomplished 
the  escape  of  further  acid  chyme  is  permitted.  This  regulatory  action 
prevents  disorder  in  the  progress  of  digestion  and  at  the  same  time 
insures  regularity  in  the  transition  from  the  acid  gastric  digestion  to 
the  alkaline  intestinal  one. 

THE  NERVOUS  CONTROL  OF  THE  STOMACH. 

As  known  to-day,  the  nerve-supply  to  the  stomach  is  from  both 
the  cerebro-spinal  system  and  the  sympathetic;  its  connection  with 
the  former  is  through  the  medium  of  the  vagi,  with  the  latter  by  the 
splanchnics  through  the  solar  plexus.  The  fibers  of  both  systems  as 
distributed  to  the  gastric  muscles  are  rionmedullated.  The  functions 
of  the  vagi  have  been  conclusively  proved  to  be  motor,,  for  when  they 
are  stimulated  by  chemical,  thermal,  or  other  irritants  there  results 
a  peristalsis  throughout  the  whole  viscus.  On  the  contrary,  the  fibers 
from  the  sympathetic  system  are  inhibitory ;  when  they  are  stimulated, 
peristalsis  is  stopped  and  there  is  dilatation  of  the  sphincter  pylori. 
The  stomach  also  has  movements  of  its  own  independent  of  the  central 
nervous  system. 

THE  GASTRIC  JUICE. 

Gastric  juice  mixed  with  food  and  water  can  readily  be  obtained 
by  the  gastric  sound  or  stomach-pump.  Pure  gastric  juice  cannot  be 
procured  thus,  for  when  the  stomach  is  empty  the  flow  of  gastric  juice 
ceases  and  any  surplus  remaining  in  the  stomach  seems  to  be  reab- 
sorbed.  Its  flow  is  begun  again  only  as  the  result  of  stimuli;  the 
natural  ones  and  those  producing  what  alone  may  be  termed  normal 
gastric  juice  are  food  and  drink. 

Normal  gastric  juice  has  been  procured  by  feeding  an  animal 
a  fictitious  meal.  In  this  process  the  food  swallowed  does  not  reach 
the  stomach,  but  passes  out  of  the  oesophagus  through  a  fistula.  The 
eating  has  the  power  to  excite  reflexly  the  flow  of  the  secretion. 

Gastric  juice  thus  obtained  from  a  dog  is  "a  clear,  colorless, 
limpid  fluid,  very  acid,  and  peptic  in  nature.  The  liquid  is  practically 
odorless;  if  there  is  any  odor  at  all  present  it  is  characteristic  of  the 
animal.  Its  specific  gravity  differs  very  little  from  that  of  water." 

The  largest  constituent  of  the  gastric  juice  is  water.  In  man  and 
animals  it  is  remarkable  to  note  the  small  quantities  of  solid  matters 
present  and  then  view  the  immense  amount  of  work  done  by  them  in 
the  digestive  processes.  Of  the  solids  present,  about  half  are  inorganic 


DIGESTION.  61 

salts;  the  remaining  portion  comprises  the  organic  ferment,,  or 
enzyme,  present  in  gastric  juice — pepsin. 

The  reaction  of  gastric  juice  is  undoubtedly  acid,  caused  by  the 
presence  of  free  hydrochloric  acid  (0.2  per  cent.).  In  the  pure  secre- 
tion, free  from  food,  it  has  been  demonstrated  that  the  only  acid  is 
hydrochloric.  Acid  is  necessary,  for  the  active  ferment  of  gastric 
juice,  pepsin,  can  act  only  in  an  acid  medium.  During  digestion, 
lactic,  acetic,  butyric,  and  other  acids  are  often  present,  due  to  putre- 
factive changes  and  the  presence  of  bacteria.  Pepsin  can  act  in  the 
presence  of  these  acids  as  media,  but  not  very  well. 

Schmidt's  analysis  of  the  composition  of  gastric  juice  is  as 
follows : — 

Water  ..  .' 994.40 

Solid  residue  .  ,  5.60 


1000.00 
Organic  matter: 

Pepsin   3.19 

Inorganic  matter: 

Chloride  of  sodium 1.46 

Chloride  of  potassium 0.55 

Chloride   of  calcium 0.06 

Free  hydrochloric  acid 0.20 

Phosphate  of  calcium ^ 

Prosphate  of  magnesium L   0.12 

Phosphate  of  iron J 

Secretion  of  the  Gastric  Juice. 

Imbedded  in  the  mucous  membrane  of  the  walls  of  the  stomach 
are  two  sets  of  secretory  apparatuses :  the  cardiac  and  pyloric  glands. 
Naturally,  the  products  of  these  glands  differ  somewhat  in  their  char- 
acters ;  so  that  the  gastric  secretion  as  a  unit  is  a  mixed  body,  or  solu- 
tion. This  "mixed"  gastric  juice  is  a  secretion  compound  of  a  very 
small  percentage  of  free  hydrochloric  acid  together  with  the  proteolytic 
ferment,  pepsin,  in  a  rather  saline  solution.  We  know  that  the  pepsin, 
for  instance,  of  the  gastric  juice,  is  not  found  as  such  in  the  blood  and 
requiring  only  to  be  filtered  from  the  same  for  use,  but  that  it  is  the 
result  of  the  activity  of  the  cells  and  yielded  by  them. 

A  characteristic  microscopical  feature  of  the  cells  of  secretory 
glands  in  general  is  that  the  protoplasmic  portions  are  crowded  with 
fine  granular  bodies  before  secretion,  but  that  during  and  particularly 
after  secretion  their  numbers  are  very  perceptibly  diminished.  From 


62  PHYSIOLOGY. 

this  it  was  inferred  that,  while  the  granules  might  not  in  themselves 
represent  the  important  ingredients  of  the  various  secretions,  yet  they 
were  responsible  and  directly  concerned  in  their  manufacture. 

The  cardiac  glands  are  composed  of  two  distinctive  types  of  cells : 
columnar  epithelium  lining  the  lumen  and  the  large  spherical  or 
oval  cells  located  on  the  periphery.  The  former  are  termed  chief,  or 
central,  the  latter  parietal,  cells. 

The  pyloric  glands  are  constructed  of  but  the  one  kind,  epithelial 
in  nature,  similar  to  those  found  in  the  cardiac  cells  and  termed 
chief,  or  central. 

The  central  cells  of  both  the  cardiac  and  pyloric  glands  are  found 
to  be  heavily  charged  with  minute  granules  before  digestion ;  in  fact, 
such  numbers  are  present  as  to  interfere  with  the  staining  of  the  cells 
with  aniline  dyes  because  of  the  protoplasm  being  obscured.  During 
secretion  some  of  the  granules  are  discharged  into  the  lumen,  pre- 
sumably through  the  protoplasmic  movements  of  the  cells  as  agents 
or  media.  After  digestion,  therefore,  the  cells  show  a  difference, 
principally  in  that  there  is  a  decrease  in  the  number  of  granules 
present,  manifested  by  either  a  clear  path  along  the  periphery  or  by  a 
shrunken  appearance  of  the  cells  with  fewer  granules.  The  materials 
for  the  formation  of  these  granules  is  taken  by  the  cells  from  the 
lymph  which  constantly  bathes  them  and  through  the  influence  of  the 
protoplasm  manufactured  into  granules. 

The  central  are  the  cells  which  are  directly  concerned  in  yielding 
the  very  important  and  proteolytic  element  of  the  gastric  juice,  the 
pepsin.  Without  its  presence  in  an  acidulated  medium,  the  normal 
processes  of  proteolysis  are  unable  to  be  accomplished  in  the  stomach. 
These  granules  are  not  pure  pepsin  to  be  passed  along  the  lumen  and 
so  enter  the  composition  of  the  gastric  juice,  but  are,  rather,  a  zymo- 
gen  substance  acting  as  a  precursor  and  which  is  readily  converted 
into  pepsin  through  the  influence  of  the  acid.  To  this  intermediate 
substance  has  been  given  the  name  pepsinogen. 

The  large  oval  or  parietal  cells  also  contain  granules  which  are 
very  few  in  number  and  small  in  size,  though  quite  distinct.  These 
are  very  constant  in  quantity,  the  cells  showing  mainly  differences  in 
size.  Thus,  before  secretion  they  are  swollen,  afterward  shrunken. 
They  are  frequently  termed  oxyntic,  as  they  are  thought  to  secrete 
hydrochloric  acid,  one  of  the  essential  compounds  of  the  gastric  secre- 
tion. The  exact  process,  however,  is  still  shrouded  in  mystery.  It 
is  thought  to  result  from  a  simple  process  of  diffusion  in  the  parietal 
cells  of  chlorides  taken  from  the  blood,  for  during  secretion  the 


DIGESTION.  G3 

quantity  of  chlorides  leaving  the  blood  through  the  kidneys  is  dimin- 
ished. Maly's  theory  with  regard  to  this  is  very  satisfactory.  In  it 
he  claims  that  the  acid  originates  by  the  interaction  of  the  calcium 
chloride  with  the  disodium  hydrogen  phosphate  of  the  blood.  The 
interaction  is  simplified  by  the  following  equation  of  Maly's: — • 

2Na2HP04  +  3CaCl2  =  Ca8(P04)2  +  4iSTaCl  +  2HC1 

Disodium  Calcium  Calcium  Sodium  Hydro- 

hydrogeu  chloride.  phosphate.  chloride.  chloric 

phosphate.  acid. 

Formed  in  the  central  cells  is  another  zymogen  than  pepsinogen, 
which,  when  mixed  with  acid,  produces  an  enzyme,  or  ferment,  known 
as  rennin.  This  ferment  has  the  power  to  coagulate  milk,  forming 
casein.  Eennin  is  found  wherever  pepsin  is  manufactured,  although 
distinctly  different  in  character  and  action.  There  are  vegetable  pep- 
sins, like  papain  of  Carica  papaya  and  bromelin  of  the  pineapple. 

The  fluid  is  not  poured  out  at  the  same  rate  from  the  beginning  to 
the  end  of  digestion.  The  Mett  method  of  preparing  the  proteid  is 
to  fill  a  glass  tube,  one  to  two  millimeters  in  diameter,  with  egg- 
albumin  and  coagulate  it  at  95°  C.  The  tube  is  then  cut  into  small 
pieces  and  placed  in  1  or  2  cubic  centimeters  of  the  juice  to  be  investi- 
gated. The  law  of  Schuetz  is  as  follows:  The  quantity  of  pepsin  in 
the  compared  liquids  is  proportionate  to  the  square  of  the  rapidity  of 
digestion ;  that  is,  the  square  of  the  column  of  proteid  in  a  Mett  tube 
expressed  in  millimeters  which  the  juices  are  capable  of  digesting  in 
the  same  period  of  time.  If  one  of  the  fluids  digest  a  column  of  2 
millimeters  of  proteid  and  the  other  a  column  of  3  millimeters,  the 
relative  quantity  of  pepsin  in  each  is  not  expressed  by  the  figures  2  and 
3,  respectively,  but  by  the  squares  of  them ;  that  is,  4  and  9 ;  so  that 
the  second  liquid  is  two  and  one-fourth  times  stronger  than  the  first. 

Not  only  the  quantity  of  the  secretion  varies,  but  the  secretion 
varies  in  composition  with  a  greater  or  less  quantity  of  ferment. 
Other  properties  of  the  juice  are  likewise  varied.  In  one  and  the 
same  juice  the  different  ferments  may  suffer  variations,  running 
courses  independently  of  each  other,  a  fact  which  undoubtedly  shows 
that  the  pancreas,  which  has  a  complex  chemical  activity,  is  able  to 
furnish,  during  given  periods  of  its  secretory  work,  now  one  prod- 
uct and  now  another.  That  which  may  be  said  of  the  ferments 
may  also  be  applied  to  the  quantities  of  the  salts  in  the  juices.  The 
gastric  juice  always  has  the  same  acidity  as  poured  out  by  the  glands, 
but  on  running  over  the  walls  of  the  stomach  the  mucus  can  neu- 
tralize 25  per  cent,  of  it.  The  food  also  neutralizes  the  acid. 


G4  PHYSIOLOGY. 

At  the  beginning  of  digestion,  when  the  quantity  of  food  is  large 
and  its  external  structure  still  coarse,  the  strongest  juice  should  be 
poured  out  when  most  needed.  The  greatest  digestive  power  belongs 
to  the  juice  poured  out  on  bread,  which  might,  for  brevity,  be  called 
"bread-juice";  the  next  strongest  is  " flesh- juice,"  and  then  comes 
"milk-juice."  In  other  words,  "bread-juice"  contains  four  times  as 
much  ferment  as  "milk- juice."  Not  alone  the  digestive  power,  but 
likewise  the  total  acidity,  varied  according  to  the  nature  of  the  diet. 
Comparing  equivalent  weight,  flesh  requires  the  most  and  milk  the 
least  gastric  juice;  but  taking  equivalents  of  nitrogen,  bread  needs 
the  most  and  flesh  the  least.  The  hourly  intensity  of  gland  work  is 
almost  equal  in  the  case  of  milk  and  flesh  diets,  but  far  less  with 
bread.  The  bread,  however,  exceeds  all  others  in  the  time  required 
for  its  digestion,  and  the  duration  of  the  secretion  is  correspondingly 
protracted. 

Each  separate  kind  of  food  corresponds  to  a  definite  hourly  rate  of 
secretion,  and  calls  forth  a  characteristic  alteration  of  the  properties 
of  the  juice.  Thus,  with  flesh  diet  the  maximum  of  secretion  occurs 
during  the  first  or  second  hour,  and  in  both  the  quantity  of  juice 
furnished  is  approximately  the  same.  With  bread  diet  we  have  always 
a  sharply  indicated  maximum  in  the  first  hour,  and  with  milk  a  simi- 
lar one  during  the  second  or  third  hour.  On  the  other  hand,  the  most 
active  juice  occurs  with  flesh  in  the  first  hour,  with  bread  in  the 
second  and  third  hours,  and. with  milk  in  the  last  hour  of  secretion. 
The  point  of  maximum  outflow  as  well  as  the  whole  curve  of  secretion 
is  always  characteristic  for  each  diet.  On  proteid  in  the  form  of  bread 
five  times  more  pepsin  is  poured  out  than  on  the  same  quantity  of 
proteid  in  the  form  of  milk,  and  the  flesh-nitrogen  requires  25  per 
cent,  more  pepsin  than  that  of  milk.  These  different  kinds  of  proteid 
receive,"  therefore,  quantities  of  ferment  corresponding  to  the  differ- 
ences in  their  digestibility,  which  we  already  know  from  experiments 
in  physiological  chemistry. 

Excitants  of   Flow  of   Gastric  Juice. 

In  his  dog  adapted  for  sham  feeding  Pawlow  cut  up  meat  and 
sausage  before  the  dog,  when  he  obtained  a  great  flow  of  gastric  juice, 
more  so  than  when  he  fed  the  dog  with  them  and  they  escaped  by  the 
oesophagus.  Here  is  a^  psychic  excitation  of  the  gastric  secretion, 
which  plays  a  considerable  part  in  the  production  of  gastric  juice  in 
the  sham  feeding  experiment. 

The  appetite  is  then  the  first  and  mightiest  exciter  of  the  secre- 


DIGESTION. 


65 


tory  nerves  of  the  stomach.  A  good  appetite  in  eating  is  equivalent 
from  the  outset  to  a  vigorous  secretion  of  the  strongest  gastric  juice. 
Sham  feeding  of  five  minutes  does  not  call  forth  a  secretion  for  longer 
than  three  to  four  hours. 

Mechanical  excitation  of  the  mucous  membrane  of  the  stomach 
does  not  cause  the  flow  of  gastric  juice.  Sodium  bicarbonate  in  the 
stomach  inhibits  its  secretion.  Liebig's  extract  or  meat-broth  intro- 
duced into  the  stomach  increases  the  secretion,  of  gastric  juice.  Fat 
in  the  stomach  inhibits  the  psychic  secretory  action  of  the  stomach 
upon  meat.  The  fat  of  milk  can.  inhibit  its  digestion  to  a  certain 
extent. 

The  secretory  activity  of  the  stomach  depends  on  nervous  proc- 
esses. In  the  immense  majority  of  cases  gastric  digestion  begins  by  a 
strong  central  excitation  of  the  secretory  and  trophic  fibers  of  the 

glands. 

Secretory  Nerves  of  the  Stomach. 

In  a  dog  with  a  cannula  in  the  stomach  and  the  oesophagus 
opened  so  that  food  leaving  the  mouth  goes  through  the  opening  in  the 
oesophagus,  and  not  into  the  stomach  ("sham  feeding"),  the  swallow- 
ing of  food  caused  a  great  increase  of  flow  of  gastric  juice.  If,  now, 
the  pulmonary  and  abdominal  vagi  are  divided  on  both  sides,  then 
sham  feeding  causes  no  flow  of  gastric  juice.  These  experiments 
show  that  the  gastric  glands  receive  their  normal  impulses  to  activity 
by  means  of  nerve-fibers  in  the  vagi.  Pawlow  believes  that  secretory 
nerves  of  the  stomach  run  in  the  vagi.  Pawlow  also  excited  the  vagi 
after  a  previous  section  for  some  days  and  obtained  an  increase  of 
gastric  secretion.  Atropine  paralyzes  the  secretory  nerves  of  the 
stomach.  By  the  secretory  fibers  we  mean  those,  according  to  Hei- 
denhain,  which  stir  up  the  secretion  of  water  and  inorganic  salts  of  the 
gastric  juice.  The  trophic  fibers  are  concerned  in  the  secretion  of  the 
ferment  of  the  gastric  juice.  Sooner  or  later  after  the  taking  of  food 
the  influence  of  the  reflex  excitant  comes  into  play,  while  the  psychic 
effect  dies  out.  If  meat  has  been  eaten  the  secretory  center  will  still 
be  strongly  excited  in  a  reflex  manner  from  the  stomach  and  intestine, 
while  at  the  same  time  the  trophic  center  receives  only  weak  impulses 
from  the  peripheral  terminations  of  the  nerves  in  question.  When 
bread  is  eaten  the  reverse  happens.  After  the  cessation  of  the  psychical 
stimulus  the  secretory  fibers  are  now  only  weakly  excited  through  the 
end-apparatus;  the  trophic,  on  the  other  hand,  are  strongly  influenced. 
In  the  case  of  fat  foods  reflex  inhibitory  impulses  proceed  to  the 
centers  which  affect  the  activity  of  both  secretory  and  trophic  nerves. 


66 


PHYSIOLOGY. 


ACTION  OF  AGENTS  ON  THE  STOMACH. 

When  absolute  alcohol  or  a  strong  emulsion  of  oil  of  mustard  is 
introduced  in  the  small  stomach  (Pawlow)  there  was  an  enormous 
secretion  of  mucus. 

Ice-cold  water  in  the  large  stomach  (Pawlow)  causes  the  secre- 
tion, which  is  subsequently  produced  by  an  ordinary  meal,  to  be  less 


CEsophagus 


Fig.  5. — Dog's  Stomach.     (PAWLOW.) 

I.    A-B,   Line  of  incision.     C,  Flap  for  forming  stomach-pouch  of  Pawlow. 
IL    Vt  Cavity  of  large  stomach.     S,  Pawlow's  pouch,  or  small  stomach.     A,  A, 
Abdominal  wall. 

than  normal,  more  especially  in  the  first  hour;    here  is  a  special 
inhibitory  reflex. 

When  alcohol  is  poured  into  the  large  stomach  (Pawlow)  an 
extremely  free  secretion  of  gastric  juice  begins  in  the  small  stomach 
(Pawlow).  The  secretion  in  the  small  stomach  was  compensatory 
for  the  arrested  secretion  in  the  large  stomach. 


DIGESTION.  G7 

In  hypersecretion  of  the  stomachs  of  dogs  he  found  sodium  bicar- 
bonate to  have  a  good  effect.  In  hyposecretion  he  found  water  a 
good  agent. 

Bitters  act  in  promoting  gastric  secretion  by  exciting  a  change 
of  the  taste,  an  appetite.  The  unpleasant  taste-impressions  of  bitters 
by  contrast  awakens  the  idea  of  pleasant  ones. 

Hydrochloric  acid,  when  secreted  in  considerable  quantity,  pre- 
vents further  secretion  of  gastric  juice.  Phosphoric  acid  does  not 
inhibit.  Butyric  acid  excites  strongly  gastric  secretion. 

ACTION   OF  THE  GASTRIC  JUICE. 

The  amylolytic  action  of  the  saliva,  conversion  of  starch  into 
maltose,  was  dependent  upon  the  presence  of  ptyalin,  an  organic  fer- 
ment whose  action  is  best  carried  on  in  a  neutral  or  alkaline  medium. 
The  proteolytic  action  of  the  gastric  juice  is  due  to  the  presence  of  its 
organic  ferment,  or  enzyme, — pepsin, — in  an  acid  medium.  A  par- 
tial digestion  of  certain  foodstuffs  can  be  accomplished  in  an  acid 
solution,  if  given  sufficient  time  and  the  proper  temperature.  There 
is,  however,  a  strong  tendency  toward  putrefaction  during  the  process. 
On  the  other  hand,  pepsin  alone  is  unable  to  perform  any  dissolution 
or  digestion  of  the  foods  with  which  it  comes  into  contact.  But,  if  to 
it  a  0.2-per-cent.  solution  of  hydrochloric  acid  is  added,  proteolysis 
proceeds  quickly  and  energetically.  The  powers  of  the  gastric  juice 
cannot  be  attributed  to  the  presence,  then,  of  its  acid  or  pepsin  alone, 
but  to  a  combination  which  may  be- termed  pepsin-acid.  Thus  gastric 
digestion  is  an  acid  digestion,  and  demands  a  knowledge  of  chemistry, 
for  it  is  in  many  respects  a  chemical  act.  The  result  of  the  action 
of  gastric  juice  on  food  is  essentially  the  same  whether  the  act  takes 
place  within  the  body  or  outside  of  it.  Life  has  nothing  to  do  with  it, 
for  it  is  a  chemical  action  on  the  proteids  of  the  food.  In  the  stomach, 
then,  the  main  process  of  digestion  is  the  conversion  of  the  proteids, 
through  intermediate  stages,  into  peptones,  for  proteids  are  incapable 
of  diffusion  through  animal  membranes  in  the  act  of  absorption. 

Thus  it  can  safely  be  stated  that  the  prime  and  essential  func- 
tion of  the  gastric  secretion  is  to  dissolve  the  proteids  present  and 
convert  them  into  peptones. 

Gastric  juice  exercises  no  amylolytic  influences  upon  any  starch 
present;  in  fact,  three-fourths  of  an  hour  after  a  meal,  the  action 
going  on  due  to  the  saliva  swallowed  with  the  food  is  stopped  alto- 
gether by  reason  of  traces  of  free  hydrochloric  acid  secreted  by  the 
oxyntic  cells. 


08  PHYSIOLOGY. 

There  is  a  fat-splitting  ferment  in  the  gastric  juice  of  the  fundus. 

Those  mineral  matters  which  can  be  dissolved  in  hydrochloric 
acid  'of  the  strength  of  that  found  in  the  gastric  juice  are  also  dis- 
solved in  the  stomach.  The  degree  of  solubility  and  efficiency  at- 
tained by  the  gastric  secretion  far  surpasses  that  of  simple.,  diluted 
acid)  probably  because  of  the  pepsin  found  in  the  former. 

Although  the  amylolytic  action  of  the  saliva  on  starch  takes  place 
for  a  definite  interval,  the  gelatinous  envelopes  of  the  fat-globules  and 
mineral  substances  are  dissolved  within  the  receptacle  of  the  stomach, 
yet  the  essential  and  characteristic  feature  of  the  work  to  be  done  there 
is  on  the  proteids:  converting  them  into  peptone  through  the  action 
of  proteolysis. 

The  proteids  found  in  Nature  are  very  complex  and  as  yet  not 
thoroughly  known.  However  much  they,  as  individuals,  may  differ 
in  composition,  reactions,  etc.,  yet  they  all  possess  an  inherent  tendency 
to  undergo  hydrolytic  decomposition  when  conditions  are  favorable. 
Hydration  and  cleavage  can  be  induced  by  simple  heating  in  water 
alone  raised  to  the  temperature  of  100°  C.,  for  there  results  partial 
solution  of  the  proteids  during  the  process.  The  proteolytic  process 
of  the  gastric  secretion  in  its  converting  proteids  into  peptones  is  also 
one  of  hydration  and  cleavage.  The  final  products  are  not  the  result 
of  one  simple  step,  not  the  formation  of  one  simple  body  or  substance, 
as  when  the  proteids  are  acted  on  by  heated  water  alone.  The  acid 
in  gastric  digestion  induces  a  row  of  chemical  changes  and  products, 
each  separate  and  distinct,  and  capable  of  being  recognized  by  certain 
reagents. 

By  the  action  of  pepsin-acid  the  proteid  is  first  changed  into  (1) 
syntonin,  or  acid-albumin.  By  further  action  of  the  ferment  the  acid- 
albumins  are  changed  into  (2)  proteases,  with  their  divisions  into 
primary  and  secondary  proteose.  The  proteoses  are  the  intermediate 
products  between  acid-albumins  and  peptones.  These  are  found  un- 
der various  names  in  this  group;  as,  the  proteoses  may  be  derived 
from  albumin,  when  they  are  called  albumoses;  or  from  globulin, 
when  the  name  globuloses  is  used.  The  proteoses  are  soluble  in  warm 
water,  acids,  and  the  alkalies.  They  are  only  slightly  diffusible  and 
coagulated  by  the  action  of  heat.  Nitric  acid  produces  a  white  pre- 
cipitate, which  is  colored  yellow  by  heat  and  dissolved  again.  When 
cool,  the  precipitate  occurs  again;  this  recurrence  of  the  precipitate 
upon  cooling  is  a  distinctive  feature  of  proteoses. 

By  the  continued  proteolytic  action  of  the  gastric  juice,  the 
proteoses  are  changed  into  (3)  peptones,  the  final,  diffusible  products 


DIGESTION.  G<j 

of  gastric  digestion.  They  are  simply  the  result  of  a  process  of 
hydration. 

The  peptones  are  very  diffusible,  particularly  in  acid  solution. 
The  utility  and  benefit  to  be  derived  from  that  characteristic  is  very 
evident  when  we  keep  in  mind  the  chief  aim  of  digestion :  to  render 
foodstuffs  into  soluble  conditions  so  that  they  may  be  readily  absorbed 
and  so  become  a  component  of  the  blood  and  eventually  of  the  tissues. 

The  peptones  are  soluble  in  water,  but  not  precipitated  from 
their  aqueous  solutions  by  the  addition  of  acids  or  alkalies,  or  by  boil- 
ing. In  fact,  peptones  are  never  coagulated  by  heat.  They  are  not 
precipitated  by  nitric  acid,  copper  sulphate,  ammonium  sulphate,  and 
a  number  of  other  reagents  usually  held  as  precipitants  of  proteids. 

A  cold  mixture  of  peptones  with  a  strong  solution  of  caustic 
potash  will  give,  on  adding  only  a  trace  of  cupric  sulphate,  a  decided 
pink  color.  Other  proteids  give  a  violet  color.  However,  the  chief 
and  striking  feature  of  peptones  is  their  great  diffusibility.  Other 
forms  -of  proteid  matter  pass  through  animal  membranes  with  very 
great  difficulty,  if  at  all. 

When  the  proteids  have  been  reduced  to  peptones,  they  are  ready 
for  absorption  into  the  blood  through  the  capillary  walls.  However, 
proteoses,  the  intermediate  products,  although  less  diffusible  than  pep- 
tones, find  their  way,  to  some  extent,  also,  through  the  capillary 
walls.  Experiment  has  demonstrated  that  pure  proteoses  or  even 
peptones  introduced  directly  into  the  blood  are  more  or  less  toxic, 
and  the  system  behaves  toward  them  as  foreign  bodies,  striving  to  get 
rid  of  them  as  speedily  as  possible.  From  this  it  is  evident  that 
there  must  be  some  transformation  in  the  very  act  of  diffusion  through 
the  capillary  walls,  else  the  nutritious  proteid  matters  are  not  used  in 
constructive  metamorphosis,  but  expelled  as  foreign  matters.  The 
agencies  which  act  upon  these  proteoses  and  peptones  in  some  manner 
destroy  their  toxic  tendencies  and  probably  convert  them  into  the 
serum-albumin,  or  globulin,  of  the  blood.  The  fact  that  peptones  are 
not  found  in  the  blood  and  lymph  during  or  directly  after  digestion 
confirms  this  idea,  since  peptones  are  absorbed  as  soon  as  manu- 
factured. An  excess  of  peptone  in  the  stomach-contents  would  have 
the  power  to  arrest  proteolysis  by  its  mere  presence.  A  preparation 
on  the  market  is  somatose,  a  mixture  of  albumoses  produced  by  the 
action  of  a  ferment  on  meat.  It  is  a  predigested  beef,  and  readily 
absorbed.  It  dispenses  with  so  much  fluid  as  is  necessary  in  pcp- 
tonized  milk. 


70  PHYSIOLOGY. 

Antiseptic  Action  of  the  Hydrochloric  Acid  in  Gastric  Juice. 

Besides  the  function  which  hydrochloric  acid  exercises  as  a  com- 
ponent of  the  gastric  secretion, — namely :  of  rendering  the  pepsin 
in  it  active, — it  possesses  another  very  powerful  property  as  a  dis- 
infectant and  germicide  in  that  it  can  kill  many  bacteria  that  are 
taken  in  with  the  food.  By  means  of  it  the  bacteria  producing 
putrefaction  are  killed,  and  thus  disorders  in  the  entire  constitution 
as  a  result  of  abnormal  digestion  are  prevented.  Even  when  putre- 
faction has  occurred  in  the  food  previous  to  its  entrance  into  the 
stomach,  upon  reaching  this  receptacle  it  is  stopped. 

Many  pathological  bacteria  are  likewise  destroyed  by  the  acid  in 
the  juice,  although  some,  as  the  bacillus  of  tuberculosis  and  that  of 
splenic  fever,  are  unaffected.  It  is  interesting  to  note  that  experi- 
ment has  shown  that  just  about  the  amount  and  strength  of  hydro- 
chloric acid  as  that  in  the  stomach  is  needed  outside  the  body  to 
accomplish  the  death  of  putrefactive  and  many  pathological  germs. 
Acetic  and  lactic  fermentations  are  arrested  by  mere  traces  of  hydro- 
chloric acid. 

To  epitomize:  The  general  action  of  gastric  juice  is  to  convert 
the  proteids  into  peptones  by  various  stages.  The  fats  are  split  up. 
Starch  is  unaffected. 

The  general  result  is  a  souplike  mass  in  the  stomach,  which 
undigested  food  is  passed  through  the  pylorus  into  the  duodenum  of 
the  small  intestine,  and  is  called  chyme.  The  average  time  that  food 
remains  in  the  stomach  is  about  three  hours. 

Glinzberg's  Test  for  Hydrochloric  Acid.  —  With  a  solution  of 
phloroglucin  and  vanillin  in  alcohol  mix  a  drop  of  a  0.2-per-cent.  solu- 
tion of  hydrochloric  acid;  evaporate  slowly  in  a  porcelain  capsule, 
when  a  red  color  will  appear. 

Uffelmann's  Test  for  Lactic  Acid. — Add  a  trace  of  a  solution  of 
ferric  chloride  to  a  1-per-cent.  solution  of  carbolic  acid.  This  ame- 
thyst-colored solution  will  change  to  canary  yellow  on  the  addition 
of  lactic  acid. 

VOMITING. 

Vomiting  is  a  spasmodic  rejection  of  food  from  the  stomach,  and 
is  usually  a  sign  of  some  malady.  The  ease  with  which  animals  vomit 
is  dependent  upon  the  conformation  of  the  stomach,  particularly  with 
regard  to  the  fundus,  as  well  as  the  condition  of  its  contents.  Thus, 
a  child  vomits  easily,  since  its  fundus  is  not  very  well  developed; 
with  the  adult  the  act  is  one  of  great  difficulty. 


DIGESTION.  71 

When  the  person  is  conscious,  vomiting  is  usually  preceded  by  a 
sensation  of  nausea,  during  which  the  saliva  flows  very  freely  into 
the  mouth.  While  the  food  is  being  swallowed  considerable  air  enters 
the  stomach  and  later  assists  actual  vomiting  by  helping  to  dilate  the 
cardiac  orifice.  Before  the  real  expulsion  occurs  and  during  the 
efforts  to  accomplish  the  same  a  very  deep  inspiration  is  taken  just 
as  in  the  act  of  coughing.  Immediately  the  glottis  closes  and  the 
muscles  of  the  abdomen  commence  to  contract  very  actively.  In- 
stead of  the  glottis  opening  to  permit  an  expiration,  it  remains 
tightly  closed,  thereby  holding  the  diaphragm  immovably  fixed  and 
so  furnishing  an  unresisting  plate  against  which  the  stomach  is 
pressed.  Immediately  preceding  the  pressure  brought  to  bear  upon 
the  stomach  by  the  contraction  of  the  abdominal  muscles,  there  occurs 
a  shortening  of  the  longitudinal  fibers  of  the  oesophagus,  thereby 
bringing  the  cardiac  orifice  of  the  stomach  nearer  the  diaphragm, 
to  form  a  straight  passageway  for  the  vomit  to  the  pharynx.  The 
muscles  of  the  sphincter  at  the  cardiac  orifice  are  rather  suddenly 
dilated,  forming  a  funnel-shaped  opening  at  the  beginning  of  escape, 
since  the  pylorus  usually  remains  closed.  By  the  abdominal  con- 
tractions and  slightly  assisted  by  gastric  movements  also,  some  of  the 
contents  of  the  stomach  is  forced  into  the  opening  of  the  oesophagus, 
where  its  movement  toward  the  pharynx  and  mouth  is  aided  by  con- 
tractions of  the  cesophageal  circular  fibers :  the  reverse  of  what  occurs 
when  a  bolus  of  food  is  swallowed. 

Thus  there  are  two  separate  and  distinct  acts  occurring  during 
vomiting:  (a)  the  dilating  of  the  cardiac  sphincter  and  (b)  the 
expulsive  movements  of  the  abdominal  muscles.  The  absence  of 
either  act  is  detrimental  to  the  accomplishment  of  vomiting.  The 
pyloric  gate  is  usually  closed  during  vomiting;  so  that  little  or  no 
substances  find  their  way  into  the  duodenum.  However,  when  the 
gall-bladder  is  very  full,  the  movements  of  the  surrounding  organs 
force  its  contents  into  the  duodenum  and  very  frequently  some  of  the 
bile  finds  its  way  into  the  stomach,  from  whence  it  passes  out  through 
the  oesophagus,  pharynx,  and  mouth  in  bilious  vomiting. 

That  the  expulsive  impetus  is  mainly  given  by  the  contractions 
of  the  abdominal  walls  and  not  the  gastric  movements  alone  has  been 
proved  by  experiment.  The  stomach  of  an  animal  was  excised  and 
replaced  with  a  bladder  filled  with  water  and  attached  to  the  oesoph- 
agus by  means  of  a  rubber  tube.  When  the  wound  was  closed  and 
an  emetic  injected,  the  contents  of  the  bladder  were  immediately 
expelled  through  the  mouth. 


72  PHYSIOLOGY. 

Vomiting  is  normally  considered  to  be  a  reflex  action,  although 
in  some  instances  vomiting  may  proceed  at  will  or  be  acquired  after 
some  practice.  The  afferent  nerves  are  principally  the  fifth,  the 
glosso-pharyngeal,  and  the  vagus.  The  center  of  vomiting  is  located 
in  the  medulla  oblongata.  The  efferent  impulses  are  conveyed  by  the 
vagi  to  the  stomach,  phrenics  to  the  diaphragm,  and  various  spinal 
nerves  to  the  abdominal  muscles.  Thus  vomiting  may  arise : — 

1.  From  irritation  of  the  stomach,  as  when  this  organ  is  too  full. 

2.  From  tickling  the  vault  of  the  palate. 

3.  From  intestinal  irritation  by  worms. 

4.  From  irritation  of  the-  uterine  mucous  membrane  during  the 
first  three  months  of  pregnancy. 

5.  The  remembrance   or  sight   of   disgusting   sights,   or   patho- 
logical disorders  of  the  brain  may  cause  it,  which  proves  that  the 
brain  is  united  to  a  vomiting  center. 

6.  The  use  of  emetics,  which  do  not  all  act  alike. 

Thus,  some  emetics,  as  copper  sulphate,  mustard,  etc.,  produce 
emesis  because  of  their  irritating  effects  upon  the  peripheral  nerves  in 
the  mucous  membrane  lining  the  stomach.  Others,  like  tartar  emetic, 
apomorphine,  etc.,  attain  the  same  results  by  reason  of  their  stimulat- 
ing the  vomiting  center  in  the  medulla. 

DIGESTION  IN  THE  INTESTINES. 

When  the  food  is  converted  into  chyme  and  partially  dissolved 
by  the  gastric  juice,  "it  passes  into  the  small  intestine,  where  it  is 
subjected  to  new  reagents:  the  bile,  pancreatic  juice,  and  intestinal 
juices.  Here  the  food  is  prepared  for  absorption,  forming  what  is 
called  chyle f  which  is  rapidly  taken  up  by  the  chyliferous  vessels. 

Because  of  the  small  and  large  calibers  of  the  two  parts  of  the 
intestinal  tract,  the  portions  have  received  the  names  of  small  and 
large  intestines,  respectively.  The  small  intestine,  the  continuation  of 
the  stomach,  opens  into  the  large  intestine  by  an  orifice  which  is 
guarded  by  the  ileo-ccecal  valve.  Under  ordinary  and  normal  condi- 
tions this  valve  allows  the  passage  of  the  remnants  of  active  digestion 
to  pass  through  from  the  small  into  the  large  intestine;  very  rarely 
does  the  reverse  occur,  except  in  some  cases  of  hernia  and  other  ob- 
structions in  the  large  intestine. 

THE   SMALL   INTESTINE. 

This  tube  is  cylindrical  and  much  convoluted.  It  occupies  the 
umbilical  region  and  is  suspended  from  the  vertebral  column  by  the 


DIGESTION.  73 

mesentery.  It  measures  about  twenty-five  feet  in  length,  and  its  diam- 
eter is  about  one  and  three-fourths  inches.  As  it  continues  to  join 
the  large  intestine  it  becomes  slightly  narrower.  It  consists  of  three 
parts  :  the  duodenum,  jejunum,  and  ileum. 

The  duodenum  is  twelve  fingers'  breadth  in  length,  and  it  is 
the  widest  part  of  the  small  intestine.  It  commences  at  the  pyloric 
end  of  the  stomach  and  opposite  the  second  lumbar  vertebra;  it 
terminates  in  the  jejunum.  The  common  bile-duct  and  the  pan- 
creatic duct  perforate  the  inner  side  of  the  duodenum. 

The  jejunum  constitutes  two-fifths  of  the  small  intestine.  It 
is  wider  than  the  ileum  and  is  characterized  by  the  absence  of  the 
agminated  glands.  The  ileum  constitutes  three-fifths  of  the  small  in- 
testine, and  terminates  in  the  right  iliac  region  by  joining  the  large 
intestine  at  a  right  angle. 

Structure   of  Small   Intestine. 

Like  the  stomach,  the  intestine  has  four  coats :  ( 1 )  the  external 
serous,  (2)  the  muscular,  (3)  the  submucous,  and  (4)  the  mucous 
coat.  The  serous  coat  is  furnished  by  the  peritoneum.  The  muscular 
coat  is  composed  of  two  layers  of  pale,  unstriped  fibers,  the  external 
layer  of  longitudinal  fibers,  and  the  internal  layer  of  circular  fibers. 
The  submucous  coat  is  thinner  than  that  in  the  stomach,  but  is  also 
extensible. 

The  mucous  coat  is  thinner  and  redder  than  that  of  the  stomach, 
and,  like  it,  has  a  columnar  epithelium.  It  has  folds  of  mucous  and 
submucous  tissue,  running  in  a  transverse  direction  and  in  the  shape 
of  a  crescent,  which  are  called  the  valvulae  conniventes.  These  valv- 
ula3  are  more  abundant  in  the  upper  part  of  the  small  intestine, 
where  they  overlap  the  edges.  As  you  go  down  the  small  intestine 
you  find  the  number  of  the  valvulas  gradually  lessen,  and  in  the  ileum 
they  disappear.  These  folds  are  permanent.  The  minute  elevations 
called  villi  beset  the  mucous  membrane  of  the  small  intestine  and 
even  the  valvulje  conniventes.  They  give  a  velvety  appearance  to 
the  surface  of  the  small  intestine.  In  the  upper  part  of  the  small  in- 
testine the  villi  appear  as  fine  folds,  but  farther  down  the  intestine 
they  appear  as  flattened,  conical  projections.  The  villi  are  1/40  inch 
in  height  and  in  structure  are  appendages  of  the  intestinal  mucous 
membrane.  They  are  covered  with  a  columnar  epithelium  and  com- 
posed of  lymphoid  tissue.  Inside  of  the  villi  are  found  the  lacteal 
blood-vessels  and  a  few  unstriped  muscular  fibers.  In  the  center  of 
the  villus  the  lacteal  begins  very  near  its  extremity  as  a  blind  end. 


74  PHYSIOLOGY. 

The  unstriped  muscular  fibers  in  the  villus  run  in  a  longitudinal 
direction.  The  number  of  the  villi  has  been  estimated  to  be  about  four 
millions. 

Glands  of  the  Small  Intestine. 

There  are  four  kinds  of  glands  in  the  mucous  membrane  of  the 
small  intestine.  They  are :  duodenal,  or  B  runner's ;  glands  of  Lieber- 
kiihn;  solitary;  and  agminated  glands,  or  Peyer's  patches. 

Brunner's  glands  are  small,  racemose  glands  situated  in  the  sub- 
mucous  tissue  of  the  duodenum.  Toward  the  end  of  the  duodenum 
they  gradually  disappear. 

The  glands  of  Lieberkiihn  are  the  most  numerous  of  all  the  glands 
of  the  small  intestine,  and  they  exist  from  the  pyloric  end  to  the 
ileo-cascal  valve.  They  are  placed  in  a  vertical  direction  in  the  thick- 
ness of  the  mucous  membrane  and  open  between  the  villi.  They  are 
about  yioo  inch  in  length.  They  have  thin  walls  lined  with  a  co- 
lumnar epithelium. 

The  solitary  glands  are  found  in  all  parts  of  the  mucous  mem- 
brane of  the  small  intestine.  They  are  minute,  whitish,  oval  or 
rounded  bodies  scattered  singly  in  the  intestine.  They  are  closed 
vesicles,  and  are  situated  in  the  submucous  tissue.  They  are  lymph- 
nodules  composed  of  retiform  tissue  and  lymphocytes. 

The  agminated  glands  (Peyer's)  are  formed  of  solitary  glands, 
disposed  in  oval  patches.  Usually  there  are  fifteen  to  thirty  of  these 
patches,  from  one-half  to  two  inches  in  length,  and  one-half  inch  in 
breadth.  The  ileum  is  their  usual  habitat,  and  they  are  seated  opposite 
the  attachment  of  the  mesentery.  In  the  neighborhood  of  the  ileo- 
cascal  valve  they  are  larger  and  more  numerous.  As  the  duodenum 
is  approached  they  are  smaller  and  fewer.  In  youth  they  are  distinct, 
less  so  in  adult  life,  and  in  old  age  may  disappear.  They  are  the 
seat  of  ulceration  in  typhoid  fever.  The  arteries  of  the  small  intestine 
are  the  superior  mesenteric  and  pyloric.  The  lymphatics  are  numer- 
ous. The  nerves  are  given  off  by  the  solar  plexus.  Beneath  the 
mucous  coat  in  the  areolar  tissue  of  the  small  intestine  are  Meissner's 
ganglia.  Between  the  muscular  coats  the  ganglia  of  Auerbach  can  be 
found. 

THE   LARGE   INTESTINE. 

This  is  a  cylindrical  tube  differing  from  the  small  intestine  in 
having  a  greater  capacity  and  a  sacculated  appearance.  It  is  about 
five  feet  in  length  and  extends  from  the  ileo-ca3cal  valve  to  the  anus. 
It  encircles  the  abdomen  in  its  course.  Like  the  small  intestine,  it 


DIGESTION.  75 

is  divided  into  three  parts :  the  caecum,  colon,  and  rectum.  The  head 
of  the  colon,  the  caecum,  is  a  wide,  blind  pouch,  or  cul-de-sac,  about  two 
and  one-half  inches  in  length  and  breadth.  Toward  its  bottom  it 
curves  inwardly  and  backward  and  is  abruptly  reduced  to  a  wormlike 
prolongation — the  vermiform  appendix.  The  small  intestine  opens 
into  the  caecum,  the  orifice  being  guarded  by  the  ileo-caecal  valve.  The 
second  and  largest  part  of  the  large  intestine  is  the  colon,  and  it  ex- 
tends from  the  caecum  to  the  rectum.  It  consists  of  four  parts,  the 
ascending,  transverse,  and  descending  colon,  with  the  sigmoid  flexure. 
Its  diameter  is  greatest  at  its  commencement,  being  about  two  and  one- 
half  inches ;  but  it  gradually  lessens  to  an  inch.  The  sigmoid  flexure 
is  shaped  like  the  letter  S.  It  is  the  narrowest  part  of  the  colon.  The 
rectum  extends  from  the  sigmoid  flexure  to  the  anus.  It  is  about  seven 
inches  in  length.  When  distended  the  rectum  is  club-shaped,  being 
narrow  above  and  expanded  just  before  it  contracts  to  the  anus.  The 
anus  is  completely  surrounded  by  a  sphincter  muscle. 

Structure  of  Large  Intestine. 

The  caecum  and  colon,  like  the  small  intestine,  have  four  coats: 
the  (1)  serous,  (2)  muscular,  (3)  submucous,  and  (4)  mucous.  The 
mucous  membrane  contains  two  kinds  of  glands :  the  glands  of  Lieber- 
kiihn  and  the  solitary  glands.  The  glands  of  Lieberkiihn  are  closely 
set  together  and  give  a  peculiar  sievelike  appearance  to  the  surface  of 
the  mucous  membrane. 

Experiments  upon  the  caecum  of  the  cadaver  prove  that  the  action 
of  the  ileo-caecal  valve  is  not  dependent  upon  muscular  contraction, 
for  fluid  forced  through  the  large  intestine  rarely  passes  into  the 
ileum.  When  the  caecum  is  filled  the  dilatation  of  the  same  presses 
upon  the  folds  of  the  valve  so  as  to  squeeze  them  tightly  together  and 
thus  prevent  any  reflux  into  the  small  intestine. 

MOVEMENTS  OF  THE  INTESTINES. 

As  was  the  case  with  the  oesophagus,  the  intestines  are  composed 
of  two  muscular  coats,  an  outer  longitudinal  one  and  an  inner  circular 
one.  Movements  in  them  are  caused  by  alternate  contractions  and 
relaxations  of  adjoining  portions  of  the  tube.  To  the  characteristic 
movements  of  the  intestines  two  names  have  been  given  to  describe  two 
separate  forms :  (1)  peristaltic  and  (2)  pendular. 

Peristalsis. — By  this  term  is  implied  the  alternate  contractions 
and  dilatations  of  adjoining  segments  to  produce  a  wavelike  motion 
which  proceeds  from  its  point  of  origin  anywhere  along  the  intestinal 


76  PHYSIOLOGY. 

tract  away  from  the  stomach.  "Antiperistalsis"  is  the  term  used  to 
designate  the  movements  running  in  an  exactly  opposite  direction : 
that  is,  toward  the  stomach.  This  is  said  never  to  occur  under  normal 
conditions. 

Pendular  Movements. — These  are  the  very  slight  swinging  to-and- 
fro  oscillations,  probably  caused  by  the  contractions  of  the  longitudinal 
fibers. 

NERVE=SUPPLY  OF  THE   INTESTINES. 

The  intestines  are  supplied  with  nerves  from  the  sympathetic 
system  mainly,  with  a  few  filaments  from  the  vagus.  The  sympathetic 
ganglia  of  Auerbach  lie  between  the  two  muscular  coats  and  extend 
from  the  oesophagus  down  throughout  the  small  and  large  intestine. 
Meissner's  ganglia,  also  belonging  to  the  sympathetic  system,  lie  in  the 
submucous  coat.  The  vagi  convey  motor  impulses  to  the  intestine, 
while  the  sympathetics  mainly  convey  inhibitory,  although  they  also 
carry  motor,  impulses.  Slight  stimulation  of  the  splanchnic  calls  out 
motion,  strong  stimulation  inhibition  of  the  intestinal  movements.  I 
have  found  that,  when  the  vagus  is  divided  in  a  rabbit  and  the  cardio- 
inhibitory  fibers  are  allowed  to  degenerate  for  five  days,  electric  stimu- 
lation of  the  cut  vagus  slows  the  pendular  movement. 

I  have  found,  also,  that  eserine,  nicotine,  and  muscarine  act  on 
the  intestino-motor  ganglia,  while  atropine  and  opium  act  on  the 
intestine-inhibitory  ganglia. 

Salines  are  supposed  to  act  as  aperients  by  their  presence  in  the 
blood,  causing  an  increased  secretion  to  be  poured  out  by  the  blood- 
vessels into  the  intestinal  canal.  The  theory  of  endosmosis  has  been 
abandoned. 

PANCREAS. 

The  pancreas  is  a  long  gland  of  a  reddish-cream  color,  and  situ- 
ated behind  the  stomach.  Its  pointlike  extremity  comes  in  contact 
with  the  spleen.  It  closely  adheres  to  the  duodenum.  It  is  about 
seven  inches  in  length,  its  width  about  one  and  one-half  inches,  and 
its  thickness  about  one-half  inch.  The  right  and  large  end  is  the 
head;  its  left  free  end  is  its  tail.  The  duct  of  Wirsung,  or  the  pan- 
creatic duct,  the  size  of  a  goose-quill,  runs  the  entire  length  of  the 
gland.  Upon  leaving  the  pancreas  the  duct  penetrates  the  wall  of  the 
duodenum,  opening,  in  conjunction  with  the  common  biliary  duct, 
about  three  inches  from  the  pylorus. 

Structure. 

In  structure  the  pancreas  is  a  compound  tubular  gland,  resem- 
bling the  salivary  glands.  In  fact,  it  has  very  frequently  been  called 


DIGESTION.  77 

the  abdominal  salivary  gland.  The  lobes  are  composed  of  ducts  which 
have  been  convoluted,  terminating  in  alveoli  or  sacs  and  which  unite 
with  other  tubules  so  as  to  communicate  with  the  main  duct.  The 
small  ducts  are  lined  with  short  columnar  epithelial  cells  which  are 
smaller  than  those  of  the  salivary  glands.  The  secretory  cells  of  the 
pancreas  are  large  and  rounded,  being  distinctive  in  that  they  possess 
an  outer  portion  which  is  nearly  or  quite  homogeneous,  staining  readily 
with  dyes,  and  an  inner  portion,  very  granular,  which  does  not  stain 
easily.  The  latter  forms  about  two-thirds  of  the  cell.  When  the 
gland  is  inactive  the  cells  are  heavily  charged  with  granules  and  the 
lumen  is  almost  invisible.  When  active,  the  cells  first  swell  up  and 
press  outward  against  the  basement  membrane,  later  diminish  in  size 
as  the  granules  pass  out  through  the  now  opened  lumen,  and  so  leave 
a  large,  clear  zone.  The  presence  of  these  numerous  small  granules 
mark  the  presence  in  the  cells  of  a  zymogen,  termed  trypsinogen, 
which  is  the  precursor  of  trypsin,  the  active  ferment  of  the  pancreatic 
juice.  In  the  interalveolar  tissue  are  islets  of  small  cells  permeated 
with  a  close  network  of  convoluted  capillaries.  These  cells  are  also 
met  with  in  the  carotid  and  coccygeal  glands.  In  the  pancreas  they 
are  called  cells  of  Langerhans,  and  are  often  degenerated  in  pancreatic 
diabetes. 

The  pancreatic  blood-vessels  are  derived  from  the  splenic  and 
branches  of  the  hepatic  and  superior  mesenteric.  Its  nervous  supply 
comprises  networks  of  fibers  from  the  splenic  plexus. 

Pancreatic  Secretion  (Pawlow). 

Each  kind  of  food  determines  the  secretion  of  a  definite  quantity 
of  pancreatic  juice,  while  the  result  as  regards  ferments  is  truly  strik- 
ing. The  greatest  amount  of  proteid  ferment  is  found  in  "milk- 
juice,"  less  in  "bread-juice"  and  "flesh-juice."  The  most  amylolytic 
ferment  occurs  in  "bread- juice,"  less  in  "milk- juice"  and  "flesh-juice." 
On  the  other  hand,  "bread-juice"  is  extraordinarily  poor  in  fat- 
splitting  ferment;  "milk-juice,"  on  the  contrary,  is  very  rich,  "flesh- 
juice"  taking  an  intermediate  position.  It  is  clear  that  as  regards  the 
two  latter  ferments  the  properties  of  the  juice  correspond  with  the 
requirements  of  the  food.  The  starch-holding  diet  receives  a  juice 
rich  in  amylolytic  ferment,  and  the  fat  a  juice  rich  in  fat-splitting 
ferment. 

The  behavior  of  the  proteid  ferment  may  puzzle.  In  the  work 
of  the  gastric  glands  we  saw  the  weakest,  here  in  pancreatic  juice 
the  strongest,  ferment  poured  out  on  milk.  When,  however,  we  take 


78  PHYSIOLOGY. 

the  quantity  of  juice  into  consideration,  we  find  here  also  that  adminis- 
tration of  like  quantities  of  proteid  in  the  form  of  bread,  flesh,  and 
milk  calls  forth  a  secretion  as  regards  the  first  of  1978,  as  regards  the 
second  of  1502,  and  as  regards  the  third  of  1085  ferment  units;  that 
is  to  say,  vegetable  proteid  likewise  demands  from  the  pancreas  the 
most,  milk  and  milk  proteid  the  least,  ferment.  The  difference  be- 
tween the  stomach  and  the  pancreas  is  limited  to  this :  that  the  former 
pours  out  its  ferment  in  very  concentrated  form  upon  bread,  the  latter 
in  a  very  dilute  condition.  This  fact  strengthens  the  supposition  that 
in  the  digestion  of  bread  a  large  accumulation  of  hydrochloric  acid  has 
to  be  avoided. 

When  in  feeding  animals  the  kind  of  food  is  altered  and  the  new 
diet  maintained  for  a  length  of  time,  it  is  found  that  the  ferment-con- 
tent of  the  juice  becomes  from  day  to  day  more  and  more  adapted  to  the 
requirements  of  the  food.  If,  for  example,  a  dog  has  been  fed  for 
weeks  on  nothing  but  milk  and  bread  and  is  then  put  on  an  exclusive 
flesh  diet,  which  contains  more  proteid,  but  scarcely  any  carbohydrate, 
a  continuous  increase  of  the  proteid  ferment  in  tjie  juice  is  to  be 
observed.  The  capability  of  digesting  proteid  waxes  from  day  to  day, 
while,  on  the  contrary,  the  amylolytic  power  of  the  juice  continuously 
wanes. 

When  under  the  influence  of  a  given  diet  this  or  that  condition 
of  the  pancreas  'had  been  established  in  experiment-animals  in  charac- 
teristic form,  Pawlow  was  able,  by  altering  the  feeding,  to  reverse  it 
several  times  in  the  same  animal.  It  seems  then  that  the  gastric  and 
pancreatic  glands  have  what  may  be  called  a  form  of  instinct.  They 
pour  out  their  juice  in  a  manner  which  exactly  corresponds  both  quali- 
tatively and  quantitatively  to  the  amount  and  kind  of  food  partaken 
of.  Besides,  they  secrete  precisely  that  quantity  of  fluid  which  is  most 
advantageous  for  the  digestion  of  the  meal. 

Hydrochloric  acid  of  gastric  juice  acts  on  epithelium  of  duodenal 
mucous  membrane,  producing  secretin,  which,  when  absorbed,  greatly 
excites  pancreatic  secretion.  Fats  in  the  stomach  retard  stomachic 
secretion,  but  increase  pancreatic  secretion,  chiefly  by  a  reflex  action 
through  the  duodenum,  and  not  from  the  mucous  membrane  of  the 
stomach.  Sleep  does  not  arrest  pancreatic  secretion. 

Psychical  effect,  strong  craving  for  food  and  water,  are  common 
excitants  for  both  gastric  and  pancreatic  secretion.  The  extractives 
of  meat  excite  the  gastric  secretion,  while  acids  and  fats  excite  the 
pancreas. 

Sodium  bicarbonate  and  alkalies  inhibit  pancreatic  secretion. 


DIGESTION.  .  79 

Secretory  Nerves  of  Pancreas. 

In  nonnareotized  dogs  whose  vagus  was  divided  four  days  pre- 
viously and  whose  cardie-inhibitory  fibers  had  lost  their  irritability, 
Pawlow  irritated  the  vagus  without  pain  and  obtained  an  increased 
pancreatic  secretion.  He  found  that  vasoconstriction  of  the  pan- 
creatic vessels  prevented  the  action  of  the  vagus  on  the  pancreas,  as 
did  compression  of  the  aorta  and  pain.  He  also  found  in  the  vagus 
inhibitory  fibers  of  the  secretion,  as  well  as  secretory.  He  believes  that 
secretory  fibers  also  run  in  the  sympathetic,  not  only  for  the  pancreas, 
but  also  for  the  stomach. 

The  usual  method  of  obtaining  pancreatic  juice  for  experimental 
purposes  is  by  insertion  of  a  cannula  or  fistula  into  the  duct  of 
Wirsung.  By  this  method  practically  normal  secretion  is  procured 
whose  composition  is  variable  at  different  times,  depending  upon 
whether  the  fluid  is  collected  three  or  four  hours  or  two  or  three  days 
after  the  operation.  The  secretion  examined  shortly  after  the  opera- 
tion is  meager  in  quantity,  though  rich  in  solids ;  that  collected  a  day 
or  two  later  is  more  copious,  but  contains  a  smaller  proportion  of  solid 
constituents.  This  is  probably  due  to  inflammatory  changes  in  the 
pancreas  as  a  result  of  the  operation.  The  pancreatic  juice  examined 
is  usually  obtained  from  dogs,  human  secretions  of  the  gland  having 
been  but  rarely  analyzed  and  it  has  never  been  obtained  under  quite 
normal  conditions.  Most  experiments  are  performed  with  the  aid  of 
an  artificial  juice  made  by  mixing  a  weak  alkaline  solution  (1  per  cent, 
sodium  carbonate)  with  a  glycerin  extract  of  pancreas.  It  is  usual  to 
treat  the  pancreas  with  a  dilute  acid  several  hours  previous  to  its  being 
mixed  with  glycerin  to  convert  the  zymogen  or  mother-substance, 
trypsinogen,  into  the  ferment,  trypsin. 

Normally,  the  pancreatic  juice  is  colorless,  viscid,  and  gummy ;  it 
flows  in  large,  pearl-like  drops,  which  become  foamy  on  agitation. 
The  fluid  is  without  odor,  and  gives  to  the  tongue  an  impression  of  a 
viscid  liquid  and  a  taste  like  that  of  salt.  The  reaction  is  always 
alkaline;  its  specific  gravity  about  1.030. 

In  consequence  of  the  removal  of  a  pancreatic  tumor  Zawadski 
obtained  human  pancreatic  juice  through  the  fistula  remaining,  which 
possessed  powerful  digestive  properties,  and  found  it  to  be  made  up  of 
the  following  composition  in  a  thousand  parts:  135.9  parts  were  of 
solid  nature,  .the  remaining  ones  being  water.  Of  the  solid  portions, 
92  were  proteids,  3.4  parts  were  inorganic  in  nature,  while  the  re- 
mainder were  organic  substances  soluble  in  alcohol.  The  figures  rep- 


80  PHYSIOLOGY. 

resenting  the  quantities  of  secretion  in  twenty-four  hours  vary  con- 
siderably as  given  by  different  observers,  but  it  has  been  roughly  esti- 
mated to  average  about  8  ounces. 

The  flow  of  pancreatic  juice  is  somewhat  as  follows:  Before  the 
meal  is  finished  there  begins  the  secretion,  which  reaches  its  maximum 
point  at  about  the  third  hour.  After  this  the  secretion  sinks  till  about 
the  sixth  or  seventh  hour,  when  it  increases  to  the  ninth  or  eleventh 
hour,  only  to  sink  gradually  to  the  eighteenth  or  twentieth.  When 
the  quantity  is  greatest  the  quality  is  poorest,  and  vice  versa.  Thus 
the  function  of  the  pancreas  in  man  is  intermittent.  During  secretion 
the  gland  is  very  red,  its  vessels  dilated,  and  the  venous  blood  red. 
During  repose  the  gland  is  flat  and  of  a  pale-yellow  color,  while  its 
blood-vessels  are  contracted.  The  secretion  is  probably  caused  by 
secretin  and  the  reflex  action  due  to  the  contact  of  the  foods.  The 
pancreatic  secretion  can  be  moderated  or  suppressed  equally  by  reflex 
action,  notably  in  vomiting. 

Of  the  3.4  parts  of  an  inorganic  nature,  the  most  abundant  is 
sodium  chloride,  with  alkaline  and  earthy  phosphates  and  alkaline 
carbonates.  The  alkalinity  of  the  juice  is  due  principally  to  the  phos- 
phates of  sodium.  Pilocarpine  increases  the  secretion,  while  atropine 
diminishes  it. 

The  organic  matters  of  the  pancreatic  juice  comprise  four  principal 
enzymes  or  ferments.  They  are:  (1)  trypsin,  (2)  amylopsin,  (3) 
steapsin,  and  (4)  a  milk-curdling  ferment. 

Trypsin,  a  very  important  constituent  of  the  pancreatic  secretion, 
is  much  like  pepsin  of  the  gastric  juice,  in  that  it  is  a  proteolytic 
enzyme  acting  on  the  proteids  and  transforming  them  into  peptones 
through  intermediate  stages.  However,  its  fermentative  powers  are 
much  stronger  and  its  range  of  activity  extends  over  more  space  than 
do  those  "of  pepsin.  Although  pepsin  and  trypsin  possess  many  prop- 
erties in  common,  yet  they  are  distinctly  different  and  separate  bodies. 
The  main,  characteristic  difference  is  that  pepsin  requires  an  acid 
medium  for  its  activity,  while  trypsin  acts  and  performs  its  functions 
best  in  an  alkaline  solution  whose  strength  ranges  from  0.5  to  1  per 
cent.  Experiment  has  proved  that  trypsin  can  act  in  a  neutral  or  very 
slightly  acid  medium. 

A  remarkable  feature  of  trypsin  is  the  large  and  rapid  transfor- 
mation of  proteid  matter  of 'any  kind  into  peptone  which  it  produces 
by  means  of  only  a  moderately  strong  solution.  Thus,  it  is  a  very 
capable  body  to  take  up  the  work  of  proteolysis  where  the  pepsin  of  the 
gastric  juice  left  it,  since  it  is  particular^  a  peptone-forming  ferment. 


DIGESTION.  gi 

As  the  final  products  of  pepsin-proteolysis,  there  resulted  peptones. 
When  these  come  into  contact  with  the  pancreatic  juice,  they  were 
quickly  broken  down  into  simple,  crystalline  bodies,  as  leucin,  tyrosin, 
aspartic  acid,  and  arginin. 

Like  pepsin,  the  proteolytic  action  of  trypsin  is  one  of  contact 
also,  only  it  displays  its  powers  more  remarkably  and  energetically, 
in  that  it  needs  no  environing  bodies  to  set  it  in  action  other  than 
water,  the  proteid  matters,  and  temperature  equal  to  that  of  the 
body.  Trypsin  displays  no  digestive  powers  on  nuclein,  keratin,  or 
starches. 

Hydrochloric  acid  quickly  destroys  trypsin  unless  there  is  great 
excess  of  proteid  substances  present,  which  means  that  the  acid  is  com- 
bined with  them  and  rendered  less  active.  When  a  filled  pancreas-cell 
is  examined  the  little  granules  within  are  found  not  to  be  active  trypsin, 
but  the  precursor  or  mother  of  the  ferment.  This  zymogen,  trypsin- 
ogen,  is  readily  converted  into  the  ferment  by  the  presence  of  a  trace  of 
acid,  since  a  great  quantity  will  immediately  kill  the  newly  formed 
ferment  as  soon  as  generated. 

Amylopsin. — This  starch-splitting  ferment  converts  starch  partly 
into  dextrin,  but  chiefly  into  isomaltose  and  maltose.  During  the  first 
month  of  life  it  is  thought  that  no  amylopsin  is  formed;  hence  chil- 
dren of  that  age  should  not  be  fed  starches.  Amylopsin  differs  from 
ptyalin  in  that  it  can  digest  cellulose,  so  that  it  is  capable  of  acting  on 
unboiled  starch.  In  many  cases  the  failure  of  digestion  of  the  carbo- 
hydrates by  the  amylopsin  is  associated  with  drowsiness  after  meals 
and  slight  headache. 

The  Steapsin,  or  Fat-splitting  Ferment,  decomposes  the  neutral 
fats  into  fatty  acid  and  glycerin.  It  also  emulsifies  the  fats:  an 
activity  which  is  assisted  by  the  bile.  One  part  of  the  fatty  acids  set 
free  by  the  steapsin  combines  with  alkalies  in  the  intestine  to  form 
soap.  This  soap  favors  the  emulsification  of  the  fats.  Another  part 
of  the  fatty  acid  is  absorbed  as  such  and  combines  with  glycerin  in 
the  intestinal  wall  again  to  form  a  fat.  The  steapsin  acts  best  in  an 
alkaline  medium,  for  acids  stop  it.  Glycerin  does  not  dissolve 
steapsin;  so  that  a  glycerin  extract  is  not  suitable  for  an  experiment. 

The  Fourth  Ferment  present  in  the  pancreatic  juice  is  an  un- 
named one,  which,  like  rennin,  has  the  power  to  coagulate  milk.  It  is 
hardly  possible  that  its  powers  are  exercised  extensively,  if  at  all,  since 
the  milk  is  probably  coagulated  in  the  stomach  by  the  rennin  found 
there  before  it  ever  reaches  the  duodenum.  The  so-called  "pepton- 
izing  powders"  are  composed  of  pancreatin  and  sodium  bicarbonate. 


$2  PHYSIOLOGY. 

From  the  nature  of  the  resulting  precipitates  in  the  transforma- 
tion of  the  caseinogen  into  casein,  it  is  evident  that  the  two  ferments 
— rennin  of  the  stomach  and  that  found  in  pancreatic  juice — are 
markedly  distinct  and  dare  not  be  confounded.  Eennin  seems  to  re- 
quire the  presence  of  calcium  salts  before  it  can  produce  coagula- 
tion, which,  when  it  does  occur,  presents  the  casein  in  the  form  of  a 
coherent  clot  entangling  in  it  the  fats  present.  There  is  squeezed  out, 
as  it  were,  from  the  closely  formed  curd  a  clear,  yellowish  liquid, 
known  as  the  whey,  containing  some  proteids  with  the  salts  and  sugar 
of  the  milk. 

On  the  other  hand,  experimentation  shows  that  the  ferment  in  pan- 
creatic juice  does  not  require  the  presence  of  the  calcium  salts  for 
precipitation  of  caseinogen;  further,  that  the  precipitate  which  does 
occur  is  very  finely  granular  in  nature;  at  the  same  time  the  milk 
seems  to  undergo  no  change  in  its  fluidity  as  far  as  can  be  dis- 
tinguished by  the  naked  eye.  The  presence  of  certain  salts,  which 
entirely  check  the  action  of  rennin,  but  slightly  hinder  the  action  of 
the  pancreatic  ferment.  It  is  believed  that  this  pancreatic  casein  is 
not  a  true  casein,  for  rennin  placed  in  its  presence  has  the  power  to 
change  it  still  further,  the  resultant  product  being  identical  with 
true  casein. 

Effects  Resulting  Upon  Removal  of  Pancreas. 

It  was  in  1889  that  von  Mering  and  Minkowski  by  experiment 
upon  the  lower  animals  proved  that  removal  of  the  pancreas  was  in 
every  case  followed  by  the  appearance  of  dextrose  in  the  urine,  a  con- 
dition known  as  diabetes,  plus  those  symptoms  marking  the  absence 
of  pancreatic  secretion  in  the  intestinal  canal  during  digestion.  In 
the  blood  there  was  as  much  as  0.5  per  cent.,  while  in  the  urine  the 
8-per-cent.  mark  was  reached.  These  investigators  found  that  animals 
presented  the  identical  characteristics  as  do  human  beings  suffering 
from  the  same  disease,  namely:  an  abnormal  excretion  of  water  with 
the  appearance  in  the  urine  of  dextrose,  acetone,  and  aceto-acetic  acid. 
Another  step  was  determining  that  this  condition  is  not  due  to  want 
of  the  pancreatic  secretion  in  the  intestine  b}*"  tying  the  duct  of  Wir- 
sung  or  else  plugging  it  and  its  branches  with  paraffin,  but  allowing  the 
organ  to  remain  in  its  proper  position  in  the  body.  The  presence  of  a 
certain  proportion  of  the  whole  gland,  even  though  its  secretion  be  not 
allowed  to  reach  the  intestines,  will  prevent  diabetes;  absence  of  this 
diseased  condition  is  still  maintained  though  a  portion  of  the  gland 
be  removed  from  its  normal  position  to  be  transplanted  elsewhere. 


DIGESTION.  83 

From  these  data  it  would  seem  that  the  pancreas  possesses  virtues 
in  the  general  economy  other  than  that  of  merely  producing  pancre- 
atic juice. 

Any  disturbance  to  these  functions  is  felt,  not  only  in  the  gland 
itself,  but  throughout  the  entire  body,  since  then  its  metabolism  is 
disturbed.  Thus  is  very  clearly  established  one  other  instance  showing 
the  intimate  relation  that  each  and  every  organ  or  part  bears  to  the 
general  mechanism  of  the  entire  body  as  a  unit  and  the  consequent 
general  disturbances  following  its  disease. 

The  transfusion  of  diabetic  blood  into  a  normal  animal  fails  to 
produce  within  the  recipient  any  diabetic  symptoms.  From  this  we 
learn  that  there  was  no  accumulation  in  the  blood  of  poisonous  matter 
which  the  pancreas  was  supposed  to  remove.  From  the  facts  noted  it 
is  apparent  that  removal  of  the  pancreas  produces  diabetes  not  from 
any  influence  upon  surrounding  sympathetic  ganglia  or  hindrance 
to  passage  of  its  secretions  into  the  intestinal  canal,  but  is  caused  by 
the  removal  from  the  system  of  something,  as  yet  undetermined,  which 
something  possesses  powers  aside  from  those  employed  in  digestion. 
The  salivary  glands,  whose  structure  is  similar  to  that  of  the  pan- 
creas, when  removed  give  no  untoward  results.  When  the  struc- 
tures of  these  two  glands  are  minutely  and  carefully  examined,  it  is 
found  that  there  is  but  one  difference :  in  the  parenchyma  of  the  pan- 
creas there  are  present  little  cells, — of  Langerhans, — epithelial  in 
appearance,  richly  supplied  with  blood-vessels,  but  having  no  connec- 
tion with  the  alveoli  or  ducts  of  the  gland.  It  is  now  believed  that 
there  is  some  internal  secretion  manufactured  by  these  patches  of 
Langerhans  cells  in  the  pancreas  which  is  a  very  powerful  factor  in  the 
disintegration  of  carbohydrates,  but  whose  removal  allows  the  abnor- 
mal production  in  the  blood  and  urine  of  dextrose.  The  sugar  present 
has  been  shown  by  Dr.  Lusk  to  be  in  a  proportion  which  bears  a  fixed 
relation  to  the  nitrogen  found  in  the  urine;  hence  the  sugar  must 
arise  from  the  breaking  down  of  the  proteid  molecule  of  cells. 

Leucin,  Tyrosin,  and  Arginin. 

The  continued  action  of  the  ferment  trypsin  produces  a  chain  of 
simple  crystalline  bodies  of  a  nitrogenous  nature.  The  crystalline 
bodies  formed  are  leucin  and  tyrosin.  Leucin  crystallizes  in  the  form 
of  spheroidal  crystals;  tyrosin  in  the  form  of  fine,  silky  needles.  A 
body  called  arginin  is  also  formed  at  the  same  time.  This  body  by 
hydration  is  changed  into  urea  in  the  intestine  and  absorbed.  Drechsel 
has  estimated  that  about  one-ninth  of  the  urea  excreted  could  arise 


84  PHYSIOLOGY. 

from  this  source  alone.    Arginin  has  also  been  found  in  the  helianthus : 
a  product  of  vegetable  proteid  metabolism. 

Leucin  (C6II13X02)  is  an  a-amido-isobutylacetic  acid,  belonging 
to  the  fatty  acid  series.  It  is  always  formed  in  any  profound  decom- 
position of  proteid,,  such  as  boiling  with  dilute  acids  or  alkalies,  in 
tryptic  digestion,  or  putrefaction.  It  has  been  found  in  nearly  every 
tissue  of  the  body  in  some  proportion  or  other,  being  particularly  com- 
mon in  pathological  conditions  of  the  tissues.  It  may  be  produced 
synthetically  in  the  chemical  laboratory. 

Tyrosin  (CgH^NOg)  belongs  to  the  aromatic  group,  and  is  known 
as  oxyphenyl-amido-propionic  acid.  It  is  a  constant  associate  of  leu- 
cm.  It  is  from  tyrosin,  however,  that  cresol  and  phenol  are  formed.  » 

I  have  found  an  infusion  of  the  pancreas,  when  injected  per 
jugular,  decrease  the  pulse  and  the  arterial  tension;  afterward  the 
tension  rose. 

LIVER. 

The  largest  gland  in  the  body  is  the  liver.  Its  shape  is  that  of 
a  triangular  prism  or  ovoidal,  with  its  long  diameter  transverse.  Its 
convex  surface  is  against  the  diaphragm.  Its  concave  surface  is  in 
contact  with  the  stomach,  colon,  and  right  kidney.  The  right  and  left 
lateral  ligaments,  with  the  suspensory  ligament,  hold  it  in  position. 
It  weighs  from  three  to  four  pounds.  The  right  portion  of  the  liver 
is  much  larger  than  the  left.  It  is  also  thicker  and  extends  lower  in 
the  abdomen  and  higher  in  the  thorax.  It  is  of  a  firm  structure, 
smooth  on  the  surface,  and  of  a  reddish-brown  color.  The  liver  has 
five  lobes,  five  fissures,  five  ligaments,  and  five  vessels.  The  chief 
fissure  to  remember  is  the  transverse,  and  is  the  point  where  the  blood- 
vessels and  nerves  enter  the  liver  and  where  the  lymphatics  and  excre- 
tory duct  emerge.  The  lobes  are  the  quadrate,  caudate,  right  and 
left,  and  lobus  Spigelii,  the  most  important  being  the  right  and  left. 
The  vessels  are  the  hepatic  artery,  vein,  and  duct,  the  portal  vein,  and 
lymphatics.  The  nerves  are  derived  from  the  solar  plexus,  and  the  left 
vagus  has  some  fibers  going  to  it.  The  whole  organ  is  insheathed  in 
a  very  fine  coat  of  areolar  tissue  known  as  Glisson's  capsule. 

Structure. 

The  hepatic  substance  is  readily  torn  and  has  a  granular  appear- 
ance; these  coarse  granules,  corresponding  with  the  distinct  one 
hundred  and  five  spots  seen  on  the  surface,  are  polyhedral,  and  are  the 
lobules  of  the  liver.  These  lobules  are  yi2  inch  in  diameter.  In 
studying  the  relation  of  these  lobules  to  the  blood-vessels  and  ducts  of 


DIGESTION. 


85 


the  liver  it  is  found  that  an  extreme  branch  of  the  hepatic  vein  com- 
mences in  the  axis  of  every  lobule  and  emerges  at  its  base  to  join  a 
larger  branch.  This  connection  of  veins  and  lobules  reminds  one  of 
the  attachment  of  the  leaves  by  their  midribs  and  stems  to  the 
branches  of  trees. 

The  capsule  of  Glisson  divides  the  liver-substance  into  these 
lobules,  for  the  areolar  tissue  enters  the  transverse  fissure  of  the  liver. 

Microscopically,  each  lobule  is  made  up  of  epithelial  cells,  natu- 
rally spheroidal,  but  because  of  compression  are  more  or  less  polyg- 


18 


Fig.  6.—  Liver  of  Man.     (DuvAi,.) 

1,  Left  lobe.  2,  Right  lobe.  6,  Lobus  quadratus.  7,  Lobus  Spigelii. 
9,  Gall-bladder.  10,  Cystic  duct.  11,  Hepatic  duct.  12,  Common  biliary  duct. 
13,  Portal  vein.  14,  15,  Hepatic  veins.  16,  Inferior  vena  cava.  19,  Hepatic 

artery. 


onal.  These,  the  true  liver-cells,  are  about  Viooo  inc^  in  diameter, 
containing  protoplasm  with  large,  round  nuclei  which  have  one  or 
more  nucleoli.  The  cells  are  held  together  by  an  albuminous  cement- 
substance;  in  it  are  fine  channels  containing  the  bile-capillaries. 

The  portal  vein  also  has  its  course  in  the  portal  canals,  where  it 
divides  and  subdivides.  By  its  division  between  the  lobules  in  the 
interlobular  connective  tissue  it  forms  the  interlobular  vein.  From 
this  vein  fine  capillary  branches  are  given  off,  which  pierce  the  envelop- 


86  PHYSIOLOGY. 

ing  membrane  of  the  lobule  to  find  their  way  toward  its  center  in  a 
converging  manner.  In  their  course  to  its  center  they  pass  in  close 
proximity  to  the  hepatic  cells,  and  it  is  here  that  the  real  secretion  of 
the  bile  takes  place.  From  the  point  of  union  of  the  capillaries  in  the 
center  of  the  lobule  there  proceeds  a  single,  straight  vein,  called  the 
intralobular  vein.  Arrived  at  the  base  of  the  lobule,  this  vein  empties 
its  contents  into  the  sublobular  vein,  a  radicle  of  the  hepatic  vein, 
which  empties  into  the  inferior  vena  cava. 

The  hepatic  artery  does  not  furnish  the  blood  for  the  secretion  of 
bile.  Its  function  is  to  furnish  a  blood-supply  to  Glisson's  capsule 
and  to  the  investment  of  the  lobules  and  the  walls  of  the  bile-ducts. 

The  course  of  the  bile-ducts  is  very  similar  to  that  of  the  portal 
vein  and  hepatic  artery.  They  have  their  origin  as  a  very  fine  inter- 
cellular plexus  formed  within  the  lobule  in  the  cement-substance  join- 
ing the  hepatic  cells.  All  cells,  except  those  in  contact  with  capillary 
blood-vessels,  are  completely  girdled  with  bile-capillaries.  Intracellu- 
lar  passages  pass  from  the  bile-capillaries  into  the  interior  of  the  liver- 
cells.  After  numerous  anastomoses  the  bile-ducts  form  larger  ones,  to 
leave  the  liver  through  the  hepatic  fissure  as  two  main  branches. 
Toward  the  exit  the  bile-ducts  become  correspondingly  larger,  with 
increase  in  the  thickness  of  their  walls.  These  are  found  to  contain 
fibrous  tissue  with  bundles  of  nonstriped  muscle-fibers  plus  small 
mucus-secreting  glands.  Within  each  lobule  are  three  networks:  a 
network  of  blood-capillaries,  a  network  of  liver-cells,  and  a  network 
of  bile-capillaries. 

The  GalNbladder. 

The  gall-bladder  acts  as  the  natural  reservoir  for  storage  of  the 
bile.  It  is  a  pear-shaped  bag  of  a  musculo-membranous  texture, 
capable  of  containing  rather  more  than  a  fluidounce  and  situated  upon 
the  under  side  of  the  liver  in  a  fissure  fashioned  for  it.  It  is  about 
four  inches  long,  one  inch  at  its  fundus,  or  base. 

The  structure  of  the  gall-bladder  consists  of  three  coats :  an  outer, 
serous  coat;  a  middle,  fibrous;  and  an  inner,  mucous  coat.  The 
fibrous  coat  contains  both  circular  and  longitudinal  fibers.  The  inner 
surface  of  the  bladder  is  lined  with  mucous  membrane,  which  is  of  a 
yellowish-brown  color. 

The  hepatic  duct,  formed  by  union  of  two  bile-ducts  issuing  from 
the  liver,  is  about  one  and  one-half  inches  long.  By  its  joining  the 
cystic,  also  about  one  and  one-half  inches  in  length,  is  formed  the 
common  bile-duct,  known  as  the  ductus  communis  choledochus.  This, 


DIGESTION.  87 

the  largest  of  the  three,  is  three  inches  long,  with  the  diameter  of  a 
goose-quill,  emptying  with  the  pancreatic  duct  into  the  duodenum 
through  a  common  opening. 

Functions  of  the  Liver. 

The  liver,  being  such  an  important  gland,  naturally  occupies  a 
very  prominent  position  in  the  general  metabolism  of  the  economy. 
Its  principal  functions  are:  the  formation  of  an  internal  secretion, 
glycogen;  'the  formation  of  urea;  and,  last,  the  production  of  the 
bile,  in  which  as  a  vehicle  many  poisonous  products  within  the  body 
are  expelled. 

Bile  is  a  thick,  golden-colored  liquid  of  a  very  bitter  taste.  Its 
secretion  by  the  liver  represents  only  one  subsidiary  function  of  the 
many  performed  by  this  important  gland.  It  represents  waste  al- 
buminous matters,  together  with  coloring  pigments  and  mineral  salts 
dissolved  in  water.  Though  primarily  an  excrementitious  substance 
performing  the  necessary  functions  of  such,  it,  however,  possesses  some 
powers  to  aid  intestinal  digestion,  both  directly  and  indirectly.  These 
will  be  discussed  under  the  head  of  "Uses  of  Bile." 

The  secretion  of  bile  is  a  continuous  process,  for  a  supply,  though 
scanty,  is  constantly  passing  into  the  duodenum.  The  arrival  of 
chyme  in  the  duodenum  immediately  calls  forth  an  increased  amount, 
to  be  followed  by  a  second  increase  some  hours  later.  It  is  in  the 
intermission  between  meals  that  the  liver  is  least  active,  and  it  is  then 
that  only  a  small  supply  reaches  the  duodenum.  It  continues  during 
pains  the  most  violent,  in  intestinal  congestion,  and  in  peritoneal 
inflammations. 

Contrary  to  the  plan  of  all  the  other  secreting  and  excreting 
organs,  the  main  supply  of  blood  to  the  liver,  and  from  which  its 
secretion,  the  bile,  is  formed,  is  venous:  from  the  portal  vein.  The 
function  of  the  hepatic  artery  is  to  supply  structures  and  membranes 
only.  Since  the  portal  vein  furnishes  the  supply,  the  bile  is  secreted 
at  a  very  much  lower  pressure  and  therefore  more  slowly  than  those 
secretions  from  glands  whose  supply  is  arterial,  as  the  pancreas  and 
salivary  glands.  It  is  quite  natural  that  a  fluid  so  complex  as  the 
bile  demands  for  its  preparation  a  much  longer  period  of  time  than 
one  which  contains  only  water,  salts,  and  certain  principles  of  the 
blood.  Though  not  directly  governed  by  nerve-influences  upon  the 
portal  vein,  the  supply  to  the  liver  is  varied. 

Compared  with  the  size  of  the  liver,  the  secretion  is  small  and 
slow  and  holds  but  little  relation  to  the  mass  of  blood  traversing  it. 


88  PHYSIOLOGY. 

The  quantity  secreted  per  diem  has  been  variously  computed  at  two 
pounds.  Its  specific  gravity  in  man  averages  1.026 ;  reaction,  neutral 
or  slightly  alkaline. 

Chemical  Properties  and  Constituents  of  the  Bile. 

Bile  mixes  with  water,  producing  no  turbidity ;  heat  produces  no 
coagulation  because  of  the  absence  of  any  coagulable  proteids.  Alcohol 
precipitates  mucin,  diastase,  and  bilirubin,  if  the  latter  is  present. 
Acetic  acid  precipitates  mucus ;  lead  acetates,  the  biliary  salts.  When 
in  contact,  bile  rapidly  destroys  the  red  blood-corpuscles. 

Bile  contains  both  organic  and  inorganic  materials.  Those  or- 
ganic are  mucin,  biliary  pigments,  biliary  salts,  cholesterin,  lecithin, 
neutral  fats,  soap,  urea,  and  diastase.  In  organic  matters  are  water, 
chloride  of  sodium,  and  phosphates  of  iron,  calcium,  and  magnesium. 

The  means  by  which  the  various  components  of  the  bile  are 
formed  is  as  yet  not  thoroughly  understood.  Some  of  its  constituents 
may  exist  in  the  portal  blood;  thus  the  pigment  is  produced  by  the 
decomposition  of  the  blood.  If  haemoglobin  itself  or  substances  which 
are  capable  of  separating  the  coloring  matter  from  the  red  corpuscles 
be  injected  into  the  portal  blood,  there  is  a  proportionate  increase  in 
bile-pigment.  Biliary  acids  are  not  preformed  in  the  blood,  for  upon 
extirpation  of  the  liver  there  follows  no  appearance  of  them  in  the 
blood.  Evidently  the  hepatic  cells  must  exert  some  functions  as  yet 
not  understood. 

The  composition  of  human  bile  is  approximately  as  follows : — 


Water 


Mucin  and  pigments 1.5  1  ^  parts  in  1000. 

Bile-salts  7.5 

Solids  *{    Lecithin  and  soaps      .1.0    f     18 

Cholesterin        0.5 

Inorganic  salts 7.5 

Bile-mucin. 

The  latest  investigations  show  that  human  bile  contains  real 
mucin. 

Bile-salts. 

There  are  two  salts  of  bile,  both  having  sodium  as  a  base.  The>e 
are  glycocholate  and  taurocholate.  These  two  acids  are  very  closely 
related  to  each  other,  for  on  boiling  with  stronger  acids  a  common 
nonnitrogenous  body  is  obtained  called  cholalic  acid,  and  an  amido- 
acid  which  contains  nitrogen.  The  glycocholic  acid  gives  glycin  and 


DIGESTION.  89 

the  taurocholic  acid  gives  taurin,  which  contains  sulphur.     In  man 

these  acids  exist  in  variable  proportions.  The  bacteria  of  the  intes- 
tinal canal  break  up  the  bile-salts. 


Fig.  7.— Taurin.     (DUVAL.) 

Glycocholic  acid  is  a  monobasic  acid,  crystallizing  in  long,  fine 
needles.  Taurocholic  is  also  monobasic;  it  crystallizes  with  great 
difficulty,  forming  fine,  deliquescent  needles,  which  in  solution  have 
a  bitter-sweet  taste.  Proteid  is  the  source  of  glycin  and  taurin. 


Fig.  8.— Glycocholic  Acid.     (DuvAL.) 

Subcutaneous  and  venous  injection  of  bile-salts  cause  coma  and 
depression. 

Hay's  Sulphur  Test  for  Bile-salts. — On  the  surface  of  bile  or  a 
solution  holding  bile-salts  sprinkle  flowers  of  sulphur,  which  will  sink 
to  the  bottom  of  the  tube,  while  on  most  other  liquids  they  will  float. 


90  PHYSIOLOGY. 

The  bile-salts  lower  the  surface  tension  of  fluids  in  which  they  are 
dissolved. 

Pettenkofer's  Test  for  Bile-acids. — Take  a  small  quantity  of  cane- 
sugar  with  sulphuric  acid  and  add  to  the  bile,  when  on  slight  heating  a 
purple  color  is  produced  which  shows  absorption  bands  in  the  spec- 
trum. The  acid  on  the  cane-sugar  produces  a  body  called  furfuralde- 
hyde,  which  sets  up  a  reaction  with  the  cholalic  acid  to  produce 

the  color. 

The  Bile=pigments. 

Normally,  the  color  of  the  bile  is  due  to  the  presence  of  but  two 
bile-pigments:  bilirubin  and  biliverdin.  When  pathological,  other 
characteristic  ones  have  been  described.  Depending  upon  the  propor- 
tion of  each  present,  the  color  may  range  from  reddish  brown  to 
grass-green.  They  are  formed  from  the  haemoglobin  of  the  blood — 
the  mother  of  all  the  bile-pigments.  In  man  and  carnivora  bilirubin 
predominates  and  gives  to  the  bile  its  yellow  color;  the  green  color1 
of  that  of  herbivora  is  due  to  biliverdin. 

Bilirubin,  being  identical  with  hsematoporphyrin,  represents  the 
iron-free  pigment  of  the  bile;  its  formula  is  C16H18N~203.  This  is  the 
permanent  pigment  of  the  bile  and  may  also  appear  as  a  calcium  com- 
pound in  red  gall-stones.  When  exposed  to  the  air  and  in  an  alkaline 
solution,  it  oxidizes  very  readily,  changing  into  biliverdin;  because 
of  this,  bile,  when  standing,  assumes  a  greenish  tint. 

Biliverdin  is  present  in  all  biles  of  a  greenish  color.  It  occurs 
as  such  in  the  liver-secretion  of  herbivora,  but  may  be  obtained  by 
allowing  human  and  carnivorous  bile  to  oxidize  slowly  by  exposure  to 
the  air.  Its  formula  is  C16H18N204,  having  one  more  atom  of  oxygen 
than  bilirubin. 

When  bilirubin  arrives  in  the  intestine  the  bacteria  generate 
nascent  hydrogen,  which  reduces  it  and  generates  another  pigment,  the 
coloring  matter  of  the  faeces,  called  stercobilin.  This  stercobilin  when 
absorbed  and  excreted  in  the  urine  is  called  urobilin. 

Gmelin's  Test  for  Bile-pigments. — Add  to  some  bile  some  nitric 
acid  containing  nitrous  acid,  when  there  will  be  a  play  of  colors : 
green,  blue,  purple,  and  yellow.  These  tints  are  due  to  the  oxidation 
of  bile-pigments.  The  green  is  biliverdin;  the  blue,  bilicyanin;  the 
purple,  bilipurpurin;  and  the  yellow,  choletelin. 

Cholesterin. 

Cholesterin  is  a  monovalent  alcohol.  It  is  present  to  some  extent 
in  all  protoplasmic  structures, — blood-corpuscles, — but  particularly  in 


DIGESTION. 


91 


bile  and  nervous  tissues.  In  the  latter  it  forms  a  very  important  part 
of  myelin.  In  the  bile  it  forms  but  a  small  proportion  of  its  contents 
—from  1  to  5  per  cent.  It  is  insoluble  in  water  and  dilute  saline 
solutions,  but  readily  soluble  in  ether,  chloroform,  alcohol,  etc. ;  in  this 
respect  it  resembles  fat,  though  not  a  true  fat.  In  bile  it  is  readily  dis- 
solved, because  of  the  presence  of  bile-salts.  If  for  any  reason  the 
latter  should  be  insufficient,  the  cholesterin  passes  out  of  solution  to 
form  concretions  around  any  foreign  particles  or  previously  hardened 
concretions,  forming  a  gall-stone  combined  with  bilirubin.  Besides 
its  characteristic  crystals,  cholesterin  is  also  detected  by  various  color- 
reactions  in  the  presence  of  iodine  and  sulphuric  acid. 

The  general  presence  of  cholesterin  in  so  many  parts  and  cells 
of  the  body  leads  to  the  impression  that  it  is  a  cleavage  product  of 


Fig.  9.— Crystals  of  Cholesterin.     (DuvAL.) 

metabolism,  being  one  of  the  waste-elements  in  the  life  of  the  cell, 
especially  the  nerve-cell.  Being  absorbed  by  the  blood,  it  finds  its  way 
to  the  liver,  there  to  be  elaborated  and  so  appear  in  the  bile.  Being  an 
excrement,  it  is  not  reabsorbed,  but  is  expelled  from  the  economy  as  a 
part  of  the  faeces.  Pathological  changes  in  tissues  are  always  marked 
by  an  increased  quantity,  which  may  be  accounted  for  by  loss  of  vitality 
in  the  diseased  cells  so  that  they  are  unable  to  break  down  the 
cholesterin. 

Cholesterin  is  not  poisonous  to  animals.  Like  lecithin,  choles- 
terin is  held  in  solution  in  the  bile  by  the  bile-salts. 

Lecithin  is  found  chiefly  in  nervous  tissues,  red  corpuscles,  and 
the  bile.  When  lecithin  is  taken  by  the  mouth  it  is  broken  up  in  the 
intestine  into  cholin,  a  poisonous  alkaloid ;  but  the  intestinal  bacteria 
destroy  it  a  once,  producing  methane,  carbonic  acid,  and  nimno:iia. 


92  PHYSIOLOGY. 

Uses  of  Bile. 

In  fasting  not  a  drop  of  bile  enters  the  intestine.  Fat,  meat 
extractives,  and  the  products  of  digestion  of  egg-albumin  set  up  a  free 
discharge  of  the  fluid.  Bile  accentuates  the  activity  of  the  pancreatic 
enzymes,  especially  the  fat-splitting  ones,  the  action  of  which  was  in- 
creased twofold.  The  pancreatic  secretion  in  its  hourly  rate  corre- 
sponds closely  with  the  entry  of  bile  into  the  intestine  under  the  same 
conditions  of  diet.  The  similarity  is  most  striking.  Bile  arrests  the 
action  of  pepsin,  which  is  injurious  to  ferments  of  pancreatic  juice, 
and  favors  the  ferments  of  the  latter,  especially  the  fat-splitting  one. 

Bile  is  principally  excrementitious.  It  partly  emulsifies  the  fats 
and  contributes  to  their  solution  by  the  soap  which  the  alkalies  of  the 
bile  produce.  By  thus  rendering  the  fats  alkaline  in  part  they  are 
able  to  come  in  closer  touch  with  the  intestinal  mucous  membrane,  to 
be  absorbed  by  it.  Endosmotic  experiments  have  proved  that  the  fats 
are  Imbibed  and  traverse  more  easily  membranes  that  are  impregnated 
with  an  alkaline  solution  than  those  simply  wet  with  water.  Experi- 
mentally, when  the  bile  is  turned  out  of  its  course,  the  chyliferous 
vessels  are  not  filled  with  white,  milky  fluid,  only  one-seventh  of  the 
normal  amount  of  chyle  being  absorbed. 

As  an  excrementitious  substance,  the  bile  may  serve  as  a  medium 
for  the  separation  of  the  excess  of  carbon  and  hydrogen  from  the  blood, 
particularly  during  intra-uterine  life. 

When  the  chyme  passes  into  the  duodenum,  the  glycocholate  and 
taurocholate  of  sodium  are  broken  up  by  the  acid  in  the  chyme  to  form 
sodium  chloride,  at  the  same  time  setting  the  bile-acids  free.  Imme- 
diately they  are  precipitated,  carrying  down  with  them  the  pepsin, 
making  the  chyme  alkaline  and  more  turbid,  due  to  the  precipitation 
of  the  unpeptonized  proteids.  This  thickening  of  the  stomach  con- 
tents aids  very  materially  in  slowing  the  movements  of  the  digested 
products  through  the  intestines,  thus  giving  the  villi  and  blood-vessels 
more  ample  time  to  absorb  nutritious  substances. 

By  rendering  the  chyme  alkaline  it  aids  the  action  of  the  pan- 
creatic juice,  which  is  most  effective  as  a  digestive  agent  in  an  alkaline 
medium,  at  the  same  time  favoring  absorption,  since  alkaline  liquids 
permit  of  more  ready  osmosis. 

To  the  bile  has  been  given  the  credit  of  being  a  natural  antiseptic 
in  that  it  hinders  putrefaction  in  the  intestine.  The  bile  itself  easily 
becomes  putrid  on  standing.  How  can  it  prevent  the  putrescence,  then, 
of  the  intestinal  contents?  That  it  does  in  some  way  diminish  this 


DIGESTION.  93 

degenerative  process  is  very  evident,  for,  when  the  common  biliary 
canal  is  ligated  the  faeces  are  more  foetid  and  the  intestinal  gases  more 
abundant.  The  bile's  so-called  antiseptic  powers  must  be  accounted 
for  by  its  hastening  absorption  and  assisting  it  to  such  an  extent  that 
the  quantity  of  matter  capable  of  putrefaction  is  greatly  diminished 
in  quantity. 

It  has  been  found  that  bile  stimulates  muscles  when  in  contact 
with  them,  throwing  them  into  a  violent  state  of  tetanus,  while  at 
the  same  time  it  irritates  the  nerves.  By  this  action  the  economy 
possesses  a  natural  purgative.  By  it  as  a  stimulus  the  secretion  of  the 
intestinal  mucous  membrane  glands  is  increased  and  more  rapid  peri- 
staltic movements  of  the  intestinal  muscles  induced  to  aid  in  the 
propulsion  of  their  contents. 

Reabsorption  of  Bile=salts. 

When  it  was  ascertained  that  the  bile-salts  were  the  product  of  the 
hepatic  cells,  that  only  a  small  proportion  appeared  in  the  faeces,  with 
a  still  smaller  proportion  in  the  urine,  the  question  arose:  Is  the 
remainder  reabsorbed  by  the  intestines  to  be  again  secreted  from  the 
blood  by  the  hepatic  cells  ? 

Bile-salts  taken  by  the  mouth  produce  an  increased  flow  of  the 
bile,  which  is  at  the  same  time  higher  in  its  percentage  of  proteids. 
Dogs'  bile,  containing  normally  only  taurocholate  of  sodium,  has  been 
found  to  contain  glycocholate'  when  that  salt  had  been  injected  into 
the  animal's  blood.  Again  when  bile  has  been  taken  from  an  animal 
for  some  time  by  a  fistula,  its  quantity  of  solids  diminishes,  showing 
that  the  hepatic  cells  cannot  give  back  these  salts  to  it  when  the  portal 
blood  does  not  convey  to  them  the  materials  for  their  formation. 
From  these  and  other  facts  it  was  deduced  that  there  must  exist  in  the 
body  reabsorption  of  bile-salts. 

Antitoxic  Function  of  the  Liver. — It  was  found  that  nicotine 
added  to  the  portal  blood  of  an  experimental  circulation  through  the 
liver  soon  vanishes.  Similar  experiments  with  strychnine,  morphine, 
and  quinine  resulted  in  the  same  way.  These  alkaloids  are  not  only 
deposited  in  the  liver-cells,  but  they  experience  a  change  in  their  chem- 
ical constitution  by  which  they  lose  their  poisonous  properties.  It  is 
well  known  that  the  liver  is  a  storage  for  the  metallic  poisons  mercury, 
arsenic,  iodine,  and  antimony  for  long  periods.  The  liver  also  trans- 
forms the  bodies  developed  by  action  of  intestinal  bacteria  on  proteid. 
I  refer  to  indol  and  phenol.  Here  the  liver  exerts  a  protective  action 
against  poisoning  by  these  bodies. 


94  PHYSIOLOGY. 

The  liver  also  reduces  the  poisonous  activit}^  of  poisons  generated 
by  specific  bacteria,  as  by  the  typhoid  bacilli  and  tetanus  organism. 
The  liver  is  probably  the  seat  of  most  active  oxidations,,  and  it  is  by 
these  chemical  activities  that  it  acts  as  a  protective  agent  against 
poisons. 

Internal  Secretion  of  the  Liver  (Glycogen). — Besides  secreting 
the  bile  to  be  partly  used  in  digestion,  but  mainly  as  an  excrementitious 
substance,  the  liver  possesses  still  another  remarkable  function, 
namely:  separation  from  the  portal  blood  by  its  cells  of  a  substance 
known  as  glycogen,  or  animal  starch. 

Glycogen  exists  constantly,  though  in  very  small  proportions,  in 
protoplasm  and  animal  membranes  in  general;  also  in  white  blood- 
corpuscles  and  pus.  It  occurs  in  more  considerable  quantities  in  liver, 
muscle,  and  embryonic  tissues  after  the  third  month.  Glycogen  is  a 
white,  tasteless  powder,  soluble  in  water,  but  producing  an  opaque 
solution.  Glycogen  possesses  the  property  of  being  readily  trans- 
formed into  glucose,  to  be  ready  for  easy  oxidation.  Glycogen  with 
iodine  in  solution  gives  a  port-wine  color,  which  disappears  upon 
heating. 

Naturally  during  absorptive  processes  following  active  digestion 
portal  blood  contains  more  than  the  normal  quantity — 1  per  1000. 
At  the  very  same  time  the  blood  in  the  hepatic  vein  during  the  in- 
tervals of  absorption  of  carbohydrates  contains  2  parts  per  1000. 
Within  the  hepatic-cell  protoplasm  glycogen  is  deposited.  When  an 
excess  of  carbohydrates  are  taken,  not  all  of  the  glycogen  can  be 
absorbed,  but  passes  through  into  the  general  circulation,  to  be  depos- 
ited in  the  muscles  and  other  tissues.  Muscles  may  contain  as  much 
as  1  or  2  per  cent. 

That  sugar  should  appear  in  both  portal  and  hepatic  blood  is  not 
to  be  wondered  at  when  carbohydrates  are  fed,  but  that  it  should  still 
be  present  when  but  meats  are  given  or  when  the  portal  vein  is  ligated 
at  the  transverse  fissure,  goes  far  to  prove  that  glycogen,  or  sugar- 
forming  animal  starch,  must  be  manufactured  within  the  parenchyma 
of  the  liver.  Even  when  an  animal  is  made  to  fast  and  at  the  same 
time  perform  very  severe  muscular  work  so  that  glycogen  disappears  in 
muscles  and  liver,  its  presence  in  the  liver  is  soon  ascertained  again 
though  the  animal  be  fed  but  gelatin. 

Since  neither  glycogen  nor  sugar  appear  in  the  bile,  it  follows 
that  it,  or  some  transformed  product  of  it,  must  be  absorbed  into  the 
blood  before  it  can  serve  any  needs  in  the  economy.  From  our  data 
we  are  led  to  believe  that  the  glycogen  is  formed  and  stored  up 


DIGESTION.  95 

in  the  liver-cell  protoplasm  and  the  appearance  of  sugar  is  due  to  its 
transformation  by  liver  diastase,  to  be  absorbed  into  the  hepatic  veins. 
Glycogen  is  formed  most  abundantly  from  carbohydrate  food, 
next  from  proteids,  but  not  from  fats,  except  glycerin,  which  causes 
glycpgen  to  be  produced.  On  a  diet  rich  in  carbohydrates  the  gly- 
cogen  of  the  liver  reaches  15  per  cent.,  while  in  a  state  of  starvation 
it  may  be  so. small  as  to  escape  the  tests. 

Uses. 

The  liver  is  the  chief  storehouse  of  the  carbohydrate  material. 
Thus  the  use  of  the  glycogenic  function  of  the  liver  is  supposed  to  be 
that  of  continuously  supplying  material  which  may  be  easily  oxidized 
for  the  purpose  of  maintaining  animal  heat  and  motion.  Sugar  is  a 
very  unstable  article  in  the  presence  of  oxygen  with  albuminoid  sub- 
stances. The  sugar  becomes  oxidized,  both  in  the  blood  during  respira- 
tion as  well  as  in  the  tissues  supplied  by  the  blood. 

DIABETES. 

Diabetes  is  a  chronic  affection  characterized  by  the  constant  pres- 
ence of  grape-sugar  in  the  urine,  an  excessive  urinary  discharge,  and 
progressive  loss  of  flesh  and  strength.  Its  exact  pathology  is  as  yet 
unknown,  but  seems  to  be  intimately  associated  with  certain  nervous 
affections,  disturbed  hepatic  and  pancreatic  functions,  sexual  excesses, 
while  heredity  also  seems  to  play  an  important  role. 

Simple  Glycosuria  must  be  differentiated  from  the  disease  dia- 
betes (mellitus),  since  the  former  is  but  a  temporary  condition,  and 
not  a  disease.  When  excessive  quantities  of  sugar,  maltose,  etc.,  are 
eaten  by  a  perfectly  healthy  individual,  sugar  appears  in  the  urine, 
due  to  the  fact  that  all  of  the  absorbed  sugar  cannot  be  carried  into  the 
portal  circulation  fast  enough,  so  that  some  finds  its  way  into  the 
thoracic  duct  and  by  it  emptied  at  once  into  the  general  circulation. 
Before  reaching  the  liver,  where  it  would  be  stored  up  as  glycogen,  it 
passes  through  the  kidneys,  there  to  be  promptly  eliminated.  This 
temporary  condition  has  been  termed  simple,  or  alimentary,  glycosuria. 
Dietary  conditions  in  the  way  of  abstaining  from  starchy  and  sac- 
charine foods  will  promptly  eradicate  this  condition.  Simple  gly- 
cosuria may  also  result  from  the  inhalation  of  chloroform,  turpentine, 
use  of  chloral,  etc. ;  it  may  be  one  of  the  conditions  following  injury 
to  the  head.  Diabetic  glycosuria  differs  in  that  sugar  is  constant  and 
is  net  made  more  significant  by  quantities  present. 

We  know  from  our  study  of  the  glycogenic  function  of  the  liver 


9G  PHYSIOLOGY. 

that  glycogen  can  be  produced  from  proteids  by  synthesis  after  the 
proteid  molecule  has  been  first  broken  down. 

If  from  any  cause,  nervous  or  otherwise,  the  metabolism  of  the 
liver  is  interfered  with,  the  function  of  glycogenesis  is  disturbed,  the 
balance  broken,  with  the  result  of  the  appearance  of  sugar  in  the  urine. 

Experimental  diabetes  may  be  produced  in  animals  in  various 
ways : — 

1.  By  Diabetic  Puncture. — By  Bernard  was  it  discovered  that 
certain  lesions  to  the  cerebro-spinal  axis,  as  puncture  of  the  floor  of 
the   fourth   ventricle,   is   capable   of   producing   diabetic   conditions. 
After  puncture  the  glycogen  of  the  liver  is  so  rapidly  converted  into 
sugar  that  it  raises  the  percentage  of  sugar  in  the  blood  to  such  a 
degree  that  there  is  more  present  than  the  tissues  can  use  up,  and  thus 
some  of  it  finds  its  way  to  the  kidneys,  there  to  be  eliminated.     The 
increased  activity  of  the  hepatic  cells  in  transforming  the  glycogen 
is  believed  to  be  due  to  stimulation  of  the  vasomotor  center  in  the 
medulla  caused  by  the  puncture,  for  other  means  of  stimulating  this 
center  have  always  produced  temporary  diabetes.     In  man,  some  dis- 
eases of  the  brain,  particularly  those  in  the  medullary  region,  are 
characterized  by  diabetic  symptoms. 

2.  Adrenalin  produces  glycosuria  by  increasing  the  changes  of 
glycogen  in  the  liver  into  sugar.     lodotliyrin  when  given  to  animals 
for  a  considerable  time  occasionally  produces  glycosuria.     The  removal 
of  the  pancreas  also  causes  diabetes. 

3.  Phloridzin. — This  drug  is  a  glucoside  obtained  from  the  root- 
bark  of  cherry-trees.     Powerful  results  are  obtained  after  its  adminis- 
tration  either   by  the   stomach   or   by   subcutaneous   or   intravenous 
injection.     With  the  appearance  of  the  sugar  in  the  urine  there  is  a 
diminution  in  the  quantity  of  glycogen  in  the  liver.     If  the  drug  be 
administered  repeatedly  so  that  all  of  the  glycogen  from  the  liver  and 
other  tissues  is  entirely  used  up,  and  then  an  additional  dose  be  admin- 
istered, dextrose  will  promptly  appear. 

Phloridzin  glycosuria  is  caused  by  an  injury  to  the  renal  epi- 
thelium, allowing  it  to  become  permeable  to  the  sugar  in  the  blood. 
In  phloridzin  diabetes  the  blood  shows  a  decrease  of  sugar  in  it,  while 
in  other  cases  of  diabetes  there  is  always  an  excess  of  sugar. 

In  diabetes  the  failure  of  the  cells  of  the  body  to  burn  sugar  is 
so  great  that  the  organism  not  only  fails  to  burn  the  starches  and 
sugars  of  the  food,  but  is  unable  to  burn  completely  the  carbohydrate 
moiety  of  the  proteids  of  the  body  itself. 

To  epitomize:  Diabetes  appears  (1)  after  the  use  of  certain 
agents,  adrenalin,  iodothyrin,  and  particularly  phloridzin;  (2)  after 


DIGESTION.  97 

inhalation  of  chloroform  and  amyl  nitrite;  (3)  after  puncture  of  the 
medulla  oblongata;  (4)  by  section  of  the  spinal  cord  above  the  exit 
of  the  hepatic  nerves,  probably  by  a  paralysis  of  the  vasoconstrictors 
of  the  liver;  (5)  by  irritation  of  the  central  ends  of  the  vagus  and 
depressor;  (6)  by  extirpation  of  the  pancreas. 

The  majority  of  cases  of  true  diabetes  terminate  fatally.  Death 
is  due  to  exhaustion  and  blood  poisoning,  producing  just  previous  to 
the  end  a  condition  of  complete  coma  called  acetonaemia. 

Oxybutyric  acid  is  the  chief  acid  in  diabetic  coma.  It  is  believed 
to  be  produced  by  the  excessive  metabolism  of  proteid.  Whenever 
a  patient  passes  more  than  five  grains  of  oxybutyric  acid  daily  then 
the  danger  of  acid  intoxication  must  be  watched.  As  to  the  estimation 
of  the  oxybutyric  acid,  it  can  be  made  by  ascertaining  the  amount 
of  ammonia  excreted,  as  it  gives  a  rough  index  of  the  excretion  of  the. 
acid.  Thus,  a  daily  output  of  ammonia  of  two  grams  corresponds  to 
about  six  grams  of  the  acid.  The  treatment  of  this  diabetic  coma  is 
by  sodium  bicarbonate  by  intravenous  injection  and  by  mouth. 

CONJUGATED   SULPHATES. 

The  aromatic  products  which  are  formed  in  the  intestines — as 
indol,  skatol,  phenol,  and  cresol — are  eliminated  by  the  kidneys  in  the 
form  of  sulphates.  The  aromatic  bodies  are  absorbed  by  the  portal 
vein  and  in  the  liver  unite  with  sulphuric  acid  produced  by  the  oxida- 
tion of  the  sulphur  of  the  proteids. 

UREA  AND  URIC  ACID. 

The  liver  receives  products  from  the  muscles,  as  ammonia  car- 
bonate, and  builds  them  into  urea.  It  also  forms  uric  acid.  In  addi- 
tion it  receives  the  urea  absorbed  by  the  portal  vein  from  a  hydration 
of  arginin  in  the  intestinal  canal. 

Jaundice  is  a  discoloration  of  the  skin  due  to  the  reabsorption  of 
bile  by  the  lymphatics  of  the  liver.  This  is  usually  due  to  obstruction 
of  the  bile-ducts  by  a  catarrh,  calculus,  or  tumor.  Arsenureted  hydro- 
gen and  toluylendiamin  will  produce  jaundice. 

Influence  of  Drugs  on  Secretion  of  Bile. — Podophyllin,  aloes, 
nitrohydrochloric  acid,  ipecacuanha,  euonymin,  and  sodium  phosphate 
stimulate  the  bile-secreting  apparatus.  Other  substances,  like  calomel, 
etc.,  stimulate  the  intestinal  glands,  but  not  the  liver-cells.  The  best 
stimulant  of  the  liver  is  ox-gall,  but  it  is  important  to  remember  that 
bile  in  the  intestine  is  liable  to  be  absorbed ;  hence  it  is  best  to  combine 
a  purgative  with  it  to  carry  it  down  the  intestinal  canal. 


98  PHYSIOLOGY. 

THE  SUCCUS  ENTERICUS. 

By  most  physiologists  the  presence  of  a  certain  liquid  product 
occurring  upon  the  surface  of  the  intestinal  mucous  membrane  is 
attributed  to  the  secretory  powers  of  the  crypts  of  Lieberktihn  and 
the  glands  of  Brunner,  presumably  due  to  their  columnar  cells,  al- 
though the  real  mechanism  of  its  secretion  is  still  unknown.  To  this 
secretion  the  name  succus  entericus  has  been  commonly  given.  As 
described  by  Thiry,  it  is  "a  limpid,  opalescent,  light-yellow-colored 
fluid,  strongly  alkaline  in  reaction,  and  possessing  a  specific  gravity 
of  1.010."  It  contains  proteid  and  mucin,  while  its  great  alkalinity 
is  due  to  the  presence  of  a  considerable  quantity  of  carbonate;  the 
latter's  presence  is  easily  detected  by  the  effervescence  resulting  upon 
mixture  with  dilute  acids.  The  amount  secreted  daily  is  perhaps 
about  two  pounds.  Erepsin,  a  ferment  found  in  the  succus  entericus, 
does  not  act  on  albumins,  but  breaks  up  albumoses,  peptones,  casein, 
protamin,  and  histon,  changing  them  into  leucin,  tyrosin,  and  am- 
monia. 

The  succus  entericus  also  contains  a  ferment  like  that  in  yeast — 
invertin.  This  body  inverts  cane-sugar  into  dextrose  and  laevulose,  and 
maltose  into  two  molecules  of  dextrose.  This  inversion  is  necessary 
for  the  absorption  of  these  sugars.  The  succus  also  contains  another 
ferment  known  as  enterokinase — a  ferment  of  ferments. 

This  ferment  augments  the  activity  of  the  pancreatic  ferments, 
especially  the  trypsin,  by  converting  the  trypsinogen  of  the  pancreatic 
juice  into  trypsin.  When  dogs  are  fed  only  on  starch  and  fatty  foods, 
then  the  pancreatic  juice  contains  only  trypsinogen  with  the  object 
of  protecting  the  amylopsin  and  steapsin.  If  the  dogs  were  fed  on 
meat  exclusively,  then  the  pancreatic  juice  contained  mainly  the  fer- 
ment in  the  shape  of  trypsin.  Unlike  the  stomach,  mechanical  irrita- 
tion of  the  intestine  calls  out  increased  secretion  of  the  succus  entericus. 
But  the  intestine  has  a  special  stimulus,  and  that  is  the  pancreatic 
juice.  If  a  little  pancreatic  juice  is  inserted  into  a  loop  of  the  intes- 
tine for  half  an  hour,  then  a  fluid  will  be  secreted  containing  much 
enterokinase.  Every  cannula  introduced  into  an  intestine  acts  as  a 
foreign  body  and  excites  a  secretion  of  water,  with  the  object  of  wash- 
ing it  out  of  the  intestine,  and  the  amount  of  enterokinase  becomes 
steadily  less  and  less.  Hence  a  mechanical  stimulus  calls  out  only 
water,  and  explains  the  severe  diarrhoea  of  acute  enteritis,  while  the 
ferment  enterokinase  is  called  out  by  the  pancreatic  juice. 


DIGESTION.  99 

DIGESTION  IN  THE  LARGE  INTESTINE. 

Besides  the  changes  wrought  upon  the  foodstuffs  in  the  mouth, 
stomach,,  and  small  intestine  by  the  various  digestive  secretions  with 
their  powerful  enzymes,  there  is  still  another  more  or  less  active 
agency  in  the  form  of  certain  bacteria  which  occur  normally  in  health 
in  varying  amounts.  They  are  swallowed  by  the  mouth  with  the  food, 
drinks,  and  saliva.  The  bacteria  are  one-celled  organisms  and  are 
produced  with  marvelous  rapidity.  From  a  physiological  point  of 
view  we  are  able  to  classify  them  into  three  groups :  ( 1 )  ferment, 
(2)  chromogenic,  and  (3)  pathogenic  bacteria.  However,  only  the 
ferment  bacteria  interest  us. 

Bacteria  of  different  kinds  have  been  noticed  at  various  times 
throughout  the  entire  alimentary  canal  from  mouth  to  anus,  but  are 
more  numerous  in  the  intestines,  particularly  in  the  large  one,  where 
their  action  is  very  marked  upon  matters  reaching  it,  so  as  to  give  rise 
to  the  term  "bacterial  digestion."  In  the  stomach,  under  normal 
conditions,  the  putrefactive  activity  of  the  bacteria  is  neutralized  and 
the  germs  themselves  killed  by  the  free  hydrochloric  acid  of  the  gastric 
juice.  It  is  in  the  intestines,  where  the  secretions  are  alkaline,  that 
the  best  media  are  found  for  their  culture  and  development. 

It  has  been  suggested  that  bacterial  digestion  was  necessary  to 
the  economy,  because  it  accomplishes  so  many  things.  But  it  has  been 
shown  by  Nuttall  that,  by  removing  guinea-pig  foetuses  directly  by 
incision  from  the  uterus  and  with  antiseptic  care,  and  then  keeping 
them  in  a  sterile  chamber  receiving  sterilized  air  and  fed  on  sterile 
milk,  they  grew.  When  their  intestinal  contents  were  examined  no 
bacteria  were  found.  Hence  the  inference  that  bacteria  are  not  neces- 
sary for  good  digestion. 

The  two  chief  bacteria  are  the  lactic  acid  bacillus  and  the  colon 
bacillus.  The  former  is  found  in  the  stomach  at  times  and  the  upper 
part  of  the  small  intestine.  The  colon  bacillus  chiefly  lives  in  the 
colon.  These  bacteria  are  aerobic;  that  is,  they  consume  oxygen  in 
their  action.  Hence  they  are  powerful  reducing  agents.  Thus  they 
take  oxygen  from  bilirubin  and  form  stercobilin.  But,  although  these 
microbes  use  oxygen,  they  can  also  live  without  it.  On  proteids  the 
bacteria  produce  by  their  action  proteoses  and  peptones,  and  from 
tyrosin  the  aromatic  bodies :  phenol  and  cresol.  Indol  and  skatol  are 
derived  from  tyrosin.  On  carbohydrates  the  bacteria  act  like  ptyalin 
and  amylopsin ;  on  fats  they  act  like  steapsin,  breaking  up  lecithin  into 
cholin.  Bacteria  in  the  stomach  and  intestine  can  set  up  five  kinds  of 


100  PHYSIOLOGY. 

fermentation:  (1)  alcoholic;  (2)  acetic;  (3)  lactic;  (4)  butyric; 
and  (5)  a  form  of  fermentation  discovered  by  Drs.  Herter  and  Bald- 
win— the  oxalic  acid  variety.  These  fermentations  may  give  rise  to 
acute  and  chronic  gastritis.  In  the  intestine  the  fermentations  will 
give  rise  to  excessive  distension,  diarrhoea,  colic,  and  a  loss  of  weight 
and  strength.  The  remote  effects  of  these  fermentations  will  be  an 
increase  of  uric  and  oxalic  acid  in  the  urine  and  of  the  acidity  of  the 
urine  itself,  causing  frequent  urinations,  especially  at  night.  The 
best  indication  of  intestinal  putrefaction  is  the  aromatic  or  ethereal 
sulphates  which  appear  in  the  urine.  The  easiest  test  to  detect  the 
indoxyl  sulphate  of  potassium  is  the  indican  reaction.1  These  bac- 
teria also  help  form  the  gases  of  the  intestine  by  a  fermentation  of  the 
food. 

THE  FAECES. 

The  foods  that  have  failed  to  be  absorbed,  after  having  remained 
about  three  hours  in  the  small  intestine,  pass  into  the  large  intestine, 
where  they  remain  for  about  twelve  hours.  The  quantity  and  con- 
sistency of  that  secreted  daily  by  an  adult  varies  within  wide  marks, 
depending  upon  the  kind  of  diet  and  the  length  of  time  the  foodstuffs 
remain  within  the  intestine.  The  adult  eliminates  about  8  ounces  of 
moist  excrement  per  diem.  From  a  vegetable  diet  the  faeces  are  both 
softer  and  contain  a  higher  percentage  of  solids  than  from  a  meat  diet ; 
softer  because  their  irritations  to  the  intestinal  walls  heighten  mucous 
secretion  and  increase  peristalsis,  thereby  hastening  its  passage,  to  the 
detriment  of  absorption.  In  a  meat  diet  the  want  of  this  stimulation 
retards  defecation  to  such  an  extent  that  it  may  occur  but  once  in 
several  days.  The  stools  are  then  small  in  amount  and  dark  in  color. 
The  stimulating  action  of  vegetables  is  what  makes  them  so  valuable 
in  mixed  diets,  although  they  are  inferior  in  nutritive  value,  bulk 
for  bulk." 

Although  the  faeces  are  so  variable  quantitatively,  they  are  more 
consistent  qualitatively,  and  present  the  following  substances: — 

I.  Water. — In  health  about  75  per  cent.;    this  becomes  much 
greater  during  diarrhoea. 

II.  Indigestible  Residue  of  different  foodstuffs,  as  nuclein,  keratin 
from  epidermic  structures,  hsematin  from  hemoglobin,  ligaments  of 
meat,  cellulose  from  vegetables,  mucin,  wood-fibers,  gums,  resins,  and 
cholesterin. 

III.  Undigested  Food. — The  quantity  of  food  ingested  has  an 
effect.     The  more  one  eats,  the  more  likely  he  is  to  have  a  quantity 

1  Herter,  "Chemical  Pathology.'* 


DIGESTION.  101 

of  undigested  matters  in  the  stool.  These  undissolved  substances  are 
usually  pieces  of  vegetables,  muscle-fibers,  connective  tissue,  and  small 
quantities  of  casein  and  fat.  These  materials  help  to  accelerate  peri- 
stalsis and  so  interfere  with  a  proper  absorption  of  those  foods  that 
would  otherwise  be  readily  taken  up. 

IV.  Mucous  Epithelial  Cells. — The  microscope  shows  these  as 
present  from  the  intestinal  surface. 

V.  Derivatives  of  Bile-salts  and  Bile-pigments. — These  are  sterco- 
bilin,  cholesterin,  traces  of  bile-acids,  and  lecithin. 

VI.  Number  of  Putrid  Products,  as  skatol,  indol,  phenol,  volatile 
fatty  acids,  ammonia,  sulphureted  hydrogen,  and  methane. 

VII.  Inorganic  Salts. — These  are  salts  of  sodium,  potassium,  cal- 
cium, magnesium,  and  iron. 

VIII.  Micro-organisms. — Bacteria  of  numerous  kinds  are  present 
in  the  faeces. 

The  Color  depends  upon  the  kind  of  food  ingested;  meat  gives 
dark-brown  or  black,  and  vegetables  light-yellow,  faeces.  The  reaction 
is  normally  alkaline  in  adults,  while  in  infants  it  may  be  acid  and  yet 
not  pathological. 

Meconium  is  the  name  given  to  the  greenish-black  contents  of 
the  large  intestine  of  the  foetus  which  is  expelled  at  or  after  birth.  It 
is  chiefly  concentrated  bile  with  intestinal  epithelium.  The  coloring 
matter  is  a  mixture  of  bilirubin  and  biliverdin,  not  stercobilin. 

Defecation. — The  act  of  defecation  is  to  a  slight  extent  voluntary, 
but  in  the  main  involuntary.  In  order  that  the  faeces  may  not  stimu- 
late mechanically  the  sphincter  reflexes  so  that  they  relax  at  any  time, 
volition  plays  a  role.  For  there  is  a  center,  having  its  seat  in  the 
brain,  which  is  inhibitory  and  by  voluntary  impulses  the  individual 
is  capable  of  relaxing  or  increasing  the  contraction  of  the  external 
sphincter  ani. 

The  inhibitory  apparatus  of  the  ano-spinal  center  arises,  accord- 
ing to  the  latest  researches  that  I  have  made  upon  the  subject,  from 
the  locus  niger  of  the  crura  cerebri.  From  this  point  inhibitory  fibers 
descend,  some  of  which  commence  to  decussate  at  a  point  in  the  pons 
down  to  the  nib  of  the  calamus  scriptorius  and  then  pass  down  the 
lateral  columns.  Some  of  the  fibers  not  decussating  also  pass  down 
the  lateral  column.  This  inhibitory  apparatus  is  under  the  control  of 
a  center  in  the  cortex.  I  might  add  here  that  the  same  inhibitory 
apparatus  presides  over  the  sphincter  vaginas. 

When  a  sufficient  quantity  of  faeces  has  arrived  in  the  lower  part 
of  the  rectum  there  is,  felt  a  need  of  expelling  them.  During  defeca- 


102 


PHYSIOLOGY. 


tion  all  the  organs  situated  in  the  abdomen  are  compressed  so  that 
the  intestinal  contents  may  be  expelled,  but  the  anal  sphincter,  like  the 
cardiac  sphincter  of  the  stomach,  offers  a  resistance,  and  during  the 
violent  efforts  the  vesical  sphincter  is  relaxed,  allowing  the  urine  to 
escape.  The  sensory  nerve-endings  in  the  mucous  membrane  of  the 
rectum  carry  .impressions  to  the  ano-spinal  center  in  the  lumbar  cord, 
which  sends  out  motor  impulses  to  the  muscles  of  the  intestine.  At 


Fig.  10. — Inhibitory  Apparatus  of  Ano-spinal  Center. 

A,   B,    Locus   niger   of   cerebral    crura.     E,   F,    Inhibitory    fibers.     P,    Pons. 
M]   Medulla  oblongata.     C,   C,    Sensory  fibers.     8,   Ano-spinal   center. 

the  same  time  the  glottis  is  closed,  the  diaphragm  and  abdominal 
muscles  are  set  in  action,  and  the  act  of  defecation  is  accomplished. 

ABSORPTION  OF  FOOD  IN   THE  STOMACH. 

The  absorption  of  the  stomach  is  much  more  limited  than  one 
might  at  first  imagine,  at  the  same  time  attended  with  much  slowness. 
Water  is  practically  not  at  all,  or  with  extreme  slowness,  absorbed  in 
the  stomach,  even  though  the  blood-vessels  are  dilated,  as  during  the 
time  that  food  is  ingested.  Experiments  show  that  when  water  is 
ingested  it  is  almost  immediately  passed  through  the  pylorus  in  little 


DIGESTION.  103 

squirts  by  reason  of  the  peristaltic  movements  before  any,  practically, 
has  disappeared  into  the  vessels.  The  stomach  does  not  behave  thus 
to  all  fluids,  for  alcohol  is  very  rapidly  taken  up.  Drugs  mixed  with 
the  latter,  such  as  chloral  hydrate,  are  far  more  rapidly  absorbed  than 
when  presented  to  the  stomach  in  other  vehicles.  Concentration  plays 
a  very  prominent  part  here,  for  absorption  increases  proportionately 
until  20  per  cent,  is  reached;  the  reverse  is  true  of  the  intestines. 
Salts  are  absorbed  very  slowly.  Fats,  in  their  stay  within  the  stomach, 
are  split  up. 


Fig.  11.— Section  of  Dog's  Intestine  showing  the  Villi.     (CADTAT.) 

c,  Blood-vessels,  injected,    d,  Lacteals,  injected.    Blind  end  of  villi  enveloped 

in  a  capillary  network  of  blood-vessels. 

ABSORPTION   IN  THE  SMALL  INTESTINE. 

The  soluble  end-products  of  the  digestion  of  the  three  main  foods 
—carbohydrates,  fats,  and  proteids— appear  in  the  small  intestines  as 
glucose,  emulsified  fats,  and  peptones,  ready  for  absorption.  It  is 
here  (the  lower  two-thirds,  since  the  upper  third  is  the  site  of  main 
digestion)  that  the  chief  absorption  of  nutriment  takes  place.  The 
presence  of  the  almost  innumerable  villi,  with  their  network  of  capil- 
lary blood-vessels  and  lactcals,  the  valvulae  conniventes  to  add  more 


104 


PHYSIOLOGY. 


surface  and  at  the  same  time  to  slow  the  progress  of  the  partially 
digested  mass,  all  help  to  make  the  intestine  an  ideal  abode  for  this 
most  important  process.  The  passage  of  the  food  along  the  small 
intestine,  though  slow,  is  yet  rapid  compared  to  the  progress  in  the 
large  intestine.  Two  to  five  hours  are  consumed  from  the  time  food 
is  ingested  until  the  first  portion  passes  through  the  ileo-caecal  valve, 
but  nine  to  twenty-three  hours  until  the  last  vestige  has  made  its 
exit.  That  fats  are  absorbed  here  has  been  demonstrated  microscop- 
ically; the  sugars  and  peptones  are  known  to  be  very  rapidly  taken 
up  even  though  the  solutions  are  very  weak.  It  is  known  that  85  per 
cent,  of  proteids  disappear;  that  is,  have  been  absorbed  in  passage 
through  only  the  small  intestine. 


Fig.  12. — Diagram  of  the  Relation  of  the  Epithelium  to  the  Lacteal 

in  a  Villus.     (FuNKE.) 
The  central  axis  is  the  lacteal   surrounded  by  adenoid  tissue. 

ABSORPTION  IN  THE  LARGE  INTESTINE. 

That  considerable  absorption  takes  place  within  the  large  intes- 
tine is  vividly  impressed  when  one  considers  for  a  moment  the  con- 
sistency of  the  contents  as  they  enter  it  through  the  ileo-csecal  valve 
and  their  density  as  they  are  ejected  as  faeces.  As  they  enter  they 
are  of  the  nature  of  a  somewhat  thickened  chyme;  as  they  leave  they 
are  a  soft  solid.  By  this  alone  we  recognize  the  amount  of  water 
that  has  been  extracted.  From  an  intestinal  fistula  it  was  ascertained 
that  about  14  per  cent,  of  proteids  enter  the  large"  intestine,  while 
the  faeces  contain  but  a  very  small  percentage. 

This  rather  extensive  power  of  the  large  intestine  is  made  use  of 
clinically  by  the  medical  profession,  who  inject  into  the  large  intestine 
enemata  of  various  substances  for  the  nutrition  of  the  patient  who 
may  be  unable  to  take  nourishment  by  the  mouth.  All  in  all,  the 


DIGESTION. 


105 


results  have  been  satisfactory;    proteids  in  solution,  eggs  beaten,  or 
peptone  to  which  is  added  a  little  salt,  are  absorbed  per  rectum. 


Fig.  13.— Lacteals  of  a  Dog  during  Digestion.     ( COLIN.) 

A,  Lacteals  of  mesentery.     B,  Mesenteric  glands.     C,  Efferent  chyle-ducts. 

D,  Receptaculum  chyli. 

.  The  steapsin  of  the  pancreatic  juice  splits  up  the  neutral  fats 
into  fatty  acids  and  glycerin.  The  fatty  acids  then  unite  with  the 
alkaline  salts  of  the  intestinal  secretions  to  form  alkaline  soaps,  which 


106  PHYSIOLOGY. 

are  soluble  in  water.  These  two  products,  soap  and  glycerin,  are  ab- 
sorbed by  the  epithelial  cells  to  be,  in  their  protoplasm,  so  built  up  and 
constructed  that  neutral  fats  are  again  in  evidence.  These  fats  appear 
in  the  form  of  small  droplets  surrounding  or  becoming  mixed  with  the 
protoplasmic  granules  of  the  cells.  It  has  been  learned  that  in  feeding 
with  fatty  acids  or  with  soaps,  they  were  not  only  absorbed,  but  also 
converted  into  fats,  which  appeared  in  the  thoracic  duct. 

Bile  also  aids  the  absorption  of  fat,  since  it  is  a  typical  solvent 
medium  for  fatty  acids  and  glycerin,  and  at  the  same  time  membranes 
(and  the  mucous  membrane  is  no  exception)  moistened  by  it  allow  the 
more  ready  passage  of  fats,  very  probably  because  of  its  alkalinity. 

Absorption  of  Carbohydrates. — This  is  sometimes  considered  a 
"sugar  absorption,"  for  it  has  been  learned  that  the  carbohydrates  are 
mainly  converted  into  maltose  and  other  forms  of  sugar  by  the  enzymes 
ptyalin  and  amylopsin. 

Thus  it  can  be  said  that  carbohydrates  are  taken  up  by  the  epi- 
thelial cells  mainly  as  maltose  and  other  forms  of  sugar;  but  these 
products  are  by  their  action  and  the  aid  of  the  succus  entericus  con- 
verted into  dextrose  to  appear  as  such  in  the  blood. 

Absorption  of  Proteids. — Proteids  may  be  absorbed  by  the  stom- 
ach and  small  and  large  intestines,  but  their  main  seat  of  absorption 
is  in  the  small  intestine.  The  end-products  of  proteolysis  (proteoses 
and  peptones)  differ  from  the  ingested  proteids  mainly  in  that  they 
are  more  diffusible. 

Numerous  and  extended  experiments  all  go  to  prove  that  these 
end-products  of  proteolytic  digestion  (proteoses  and  peptones)  are 
transformed,  in  their  passage  through  the  epithelial  cells,  by  virtue 
of  their  living  protoplasm,  back  again  into  native,  coagulable  proteids 
in  the  form  of  globulins  and  albumins.  To  the  vital  properties  of  the 
living  epithelial  cell  of  the  villi  is  the  economy  indebted,  not  only 
for  absorption,  but  because  it  protects  it  from  those  toxic  effects  at- 
tending the  presence  of  peptones  in  the  blood  by  its  converting  them 
into  useful  bodies. 

The  proteoses  and  peptones  are  taken  up  directly  by  the  blood- 
capillaries  to  enter  the  systemic  circulation  directly,  the  lymphatics 
taking  little  or  no  part  in  their  absorption. 

Absorption  of  Water  and  Salts. — In  the  intestines  the  absorption 
of  water  and  inorganic  salts  is  both  very  extensive  and  very  rapid. 

The  following  resume  of  Moore's,  somewhat  changed,  gives  a  re- 
view of  the  action  of  the  ferments : — 


DIGESTION. 


107 


CLASS  OF  ENZYME. 

NAME  OF 
ENZYME. 

DIGESTIVE  FLUID 
IN  WHICH    FOUND. 

CONCISK  I>KS<  KIl'TION 
OF  SPECIFIC  ACTION. 

1.  Ptyalin. 

Saliva. 

Convert  amyloses  (  starch 
and  glycogen  )  into 

2.  Amylopsin. 

Pancreatic  juice. 

isomaltose,  accom- 
panied by  glucose. 

1.  Pepsin. 

Gastr'c  juice. 

1  .  Con  verts  proteids  into 
proteoses  and  peptones. 

Proteolytic. 

2.  Trypsin. 

•Pancreatic  juice. 

2.  Converts  proteids  into 
proteoses,  peptones, 
and  amido-acids. 

3.  Erepsin. 

Succus  entericus. 

3.  Converts     peptones 
intoleucin,  ty  rosin,  and 
ammonia. 

Fat-splitting,  or 
steatolytic. 

Steapsin. 

Pancreatic  juice. 

Splits  up  neutral  fats 
into  fatty  acids  and 
glycerin. 

Coagulating. 

1.  Rennin. 

Gastric  juice. 

1.  Coagiilates  milk,  con- 
verting caseinogen  in 
presence  of  calcium 
salts  into  casein. 

2.  Rennin. 

Pancreatic  juice. 

2.  Coagulates  milk. 

Inverting. 

Invertin. 

Succus  entericus. 

Inverts  maltose  into  dex- 
trose and  Isevulose. 

Ferment  increas- 
ing power  of 
other  ferments. 

Enterokinase. 

Succus  entericus. 

Increases  the  power  of  the 
pancreatic  ferments, 
especially  the  proteo- 
lytic,  by  converting 
trypsinogen  into  tryp- 
sin. 

CHAPTER  IV. 

ABSORPTION. 

ACCORDING  to  some  authors.,  the  absorption  of  the  economy  in  its 
entirety  consists  of  two  processes,  the  first  of  which  has  for  its  purpose 
and  aim  the  introduction  into  the  blood-stream  of  fresh  material  for 
the  nutrition  of  the  various  tissues  of  the  body.  It  is  called  absorption 
from  without,  and  has  its  seat  in  the  alimentary  canal  chiefly,  aided, 
to  some  extent,  by  the  skin  and  lungs.  The  second  process  endeavors 
to  remove  from  the  numerous  tissues  of  the  body,  by  very  gradual  meas- 
ures, the  waste-products  that  would  otherwise  accrue  everywhere  within 
the  body  as  a  resultant  of  the  use  of  its  various  tissues.  This  second 
process  is  known  as  the  absorption  that  takes  place  from  within,  and 
has  its  seat  everywhere  within  the  tissues  of  the  body. 

For  consideration  of  the  first  process,  or  absorption  from  without, 
the  reader  is  referred  to  absorption  of  food  under  the  general  head  of 
"Digestion"  (in  the  preceding  chapter).  It  was  there  noted  that 
the  ingested  foodstuffs  in  their  passage  through  the  alimentary  canal 
were  subjected  to  various  and  numerous  enzymic  and  bacterial  actions 
until  the  major  portion  of  them  was  reduced  to  certain  soluble  and 
well-defined  end-products.  Until  these  latter  were  produced  they  were 
incapable  of  serving  the  needs  of  the  body,  since  they  were  unable  to 
be  absorbed.  It  is  only  after  absorption  that  the  different  nutrient 
products  can  be  assimilated  to  become  components  of  the  living  mate- 
rials of  the  economy  for  growth  and  repair.  It  was  also  learned  that, 
though,  some  absorption  occurred  in  the  mouth,  oesophagus,  and  large 
intestine,  yet  the  main  seat  of  this  function  is  in  the  small  intestines, 
where  the  end-products  enter  the  circulation  by  the  villi  and  the  so- 
called  lacteals. 

In  turn  we  noted  the  manner  and  principal  seats  of  absorption  of 
the  fats,  carbohydrates,  proteids,  water,  and  salts.  For  many  years 
the  old  physiologists  entertained  the  view  that  absorption  of  the  end- 
products  of  digestion  from  the  alimentary  canal  was  purely  phys- 
ical; that  is,  that  the  same  laws  governed  this  bodily  function  that 
do  the  passage  of  any  liquid  with  its  contained  dissolved  substances 
(108) 


ABSORPTION.  109 

through  a  dead  membrane  placed  outside  of  the  body.  These  proc- 
esses of  osmosis  and  filtration,  as  they  were  known  to  the  physicist,  are 
to  a  small  extent  responsible  for  some  of  the  intestinal  absorption. 
But  to-day  the  newer  view  concerning  this  absorption  is  accepted, 
whereby  it  is  believed  that  the  living  epithelial  cells  of  the  lining 
mucous  membrane  of  the  small  intestine  possess  in  themselves,  as 
living  beings,  the  power  to  exert  a  selective  action  during  absorption ; 
at  the  same  time  they  modify  the  end-products  during  their  passage 
through  them.  They  change  the  peptones  into  albumins  and  unite  the 
fatty  acids  to  glycerin.  That  the  process  was  selective,  and  not  due  to 
purely  physical  laws,  was  proved  by  the  more  rapid  absorption  of  grape- 
sugar  than  sodium  sulphate,  though  the  latter  is  many  times  more 
diffusible  than  the  former. 

OSMOSIS. 

An  electrolyte  is  a  chemical  compound  which  when  molten  or  in 
solution  conducts  an  electrical  current.  When  such  a  current  passes 
through  its  solution  the  latter  undergoes  certain  changes  that  are 
grouped  under  the  name  of  electrolysis.  The  places  at  which  the 
electrical  current  enters  or  leaves  the  electrolyte  are  called  electrodes : 
"the  anode  and  cathode.  The  electrically  charged  particles,  the  aggre- 
gation of  which  constitutes  a  molecule  of  the  electrolyte,  are  called 
the  ions  of  the  electrolyte.  The  ions  which  under  the  influence  of 
the  electrical  current  migrate  to  the  anode  are  anions;  those  which 
wander  to  the  cathode,  cathions.  Thus,  for  example,  NaCl  is  an  elec- 
trolyte ;  Na  and  Cl  are  its  ions ;  Na  is  the  cathion,  01  the  anion ;  in 
the  electrolysis  of  an  NaCl  solution  the  cathion,  Na,  wanders  to  the 
cathode,  the  anion  to  the  anode.  According  to  Clausius,  the  con- 
stituents of  a  greater  or  less  number  of  dissolved  molecules  exist  in  a 
free  state  and  move  in  all  directions  through  the  solution  even  before 
the  passage  of  an  electrical  current.  Only  the  presence  of  the  free 
ions  makes  it  possible  that  such  a  solution  can  at  all  conduct  electricity. 
If  we  dissolve  crystals  of  sodium  chloride  in  water,  a  part  of  the  NaCl 
molecules  split  into  ions :  Na  and  Cl.  If  an  electrical  current  is  passed 
through  such  a  solution  the  ions  which  at  first  were  moving  in  all 
directions  are  arrested  and  drawn  to  the  poles.  An  ion  is  the  electro- 
lytic representative  of  an  atom,  but  is  theoretically  much  smaller  in 
size. 

The  function  of  ions  is  by  their  presence  in  definite  proportion 
in  each  tissue  to  preserve  the  "labile  equilibrium"  of  the  colloid  mate- 
rials of  the  protoplasm  on  which  its  activities  depend. 


110 


PHYSIOLOGY. 


Osmotic  Pressure.1 

Saw  a  Pasteur-Chamberland  filter  in  half.  The  cylinder  is  then 
dipped  in  dilute  hydrochloric  acid,  which  is  sucked  through  the  wall 
of  the  cylinder  by  a  hydraulic  airpump  in  order  to  remove  any  caolin 
dust  that  might  choke  its  pores;  then  rinse  with  water  in  a  similar 
way.  A  beaker  is  now  filled  with  a  solution  of  potassium  ferrocyanide 
(139  grains  per  liter),  the  cylinder  is  dipped  into  it,  and  the  solution 
is  sucked  through  its  wall.  After  the  cylinder  has  been  again  rinsed 
in  water  it  is  dipped  into  a  second  beaker  containing  a  copper  solution 


B 


S 

C 

^ 

m 

Water 

Sugar 
solu- 
tion 

Water 

Water 

G 


Fig.  14.  —  Osmometer. 


(249  grams  of  the  salt  per  liter),  the  inside  of  the  cylinder  being  also 
filled  with  the  solution.  A  layer  of  copper  ferrocyanide  is  deposited 
within  the  wall  of  the  cylinder,  and  this  precipitate  constitutes  the 
semipermeable  precipitation  membrane  which  is  permeable  for  water, 
but  impermeable  for  salts. 

If  we  introduce  a  sugar  solution  into  cell  C  prepared  in  this  man- 
ner and  close  it  with  the  stopper  of  rubber  (S),  which  is  perforated 
by  the  tube  AB,  then  when  C  is  dipped  into  pure  water  the  sugar  en- 


literature  consulted:    Cohen's  "Physical  Chemistry,"  1903. 


ABSORPTION. 


Ill 


deavors  to  pass  from  the  place  of  higher  concentration  (the  solution) 
to  that  of  lower  concentration  (the  water  without  the  cell).  But  this 
movement  is  opposed  by  the  semipermeable  membrane,  and  in  conse- 
quence the  sugar  exerts  a  pressure  upon  the  membrane.  Since  this 
wall,  however,  is  unyielding  and  so  resists  the  pressure,  a  pull  is 
exerted  upon  the  water  by  the  solution  which  tends  to  dilute  the  latter. 
This  comes  to  pass  when  the  solution  enters  the  tube  and  the  water 
from  G  streams  through  the  membrane  into  the  cell  and  dilutes  the 
solution.  This  process  goes  on  until  the  resulting  hydrostatic  pressure 
in  AB  prevents  the  further  entrance  of  the  water.  When  equilibrium 
has  been  established  this  hydrostatic  pressure  is  equal  to  the  osmotic 
pressure  of  the  solution.  Conversely,  however,  the  latter  may  be 
measured  by  ascertaining  the  hydrostatic  pressure  which  exists  when 
equilibrium  is  established;  with  100  grams  of  water,  containing  6 
grams  of  sugar,  the  osmotic  pressure  was  3075  millimeters  of  mercury. 

Boyle-Van't  Hoff  Law. — At  constant  temperature  the  osmotic 
pressure  of  dilute  solutions  is  proportional  to  the  concentration  of  the 
dissolved  substance.  Gay-Lussac-Van't  Hoff  law  for  dilute  solutions 
is  as  follows :  At  constant  volume  the  osmotic  pressure  of  dilute  solu- 
tions increases  as  the  temperature;  or,  also,  the  osmotic  pressure  of 
dilute  solutions  is  proportional  to  the  absolute  temperature. 

Law  of  Avogadro-Van't  Hoff. — At  the  same  osmotic  pressure  and 
the  same  temperature  equal  volumes  of  dilute  solutions  contain  the 
same  number  of  molecules.  The  same  laws  have  been  applied  to  gases. 
The  great  importance  for  the  biologist  of  the  freezing-point  determina- 
tion lies  in  the  fact  that  they  enable  him  to  ascertain  the  number  of 
molecules  dissolved  in  a  given  volume  of  any  body  fluid.  A  depression 
of  the  freezing-point  of  1/1000  degree  corresponds  to  an  osmotic  pressure 
equal  to  0.012  atmosphere.  While  chemical  analysis  can  tell  us  much 
concerning  the  composition  of  physiological  fluids,  it  cannot  yield  us 
anything  definite  concerning  the  osmotic  behavior  of  such  solutions. 
This  becomes  intelligible  when  we  remember  that  the  osmotic  pressure 
of  a  solution  is  dependent  upon  the  number  of  molecules  (+  ions)  it 
contains,  and  that  this  cannot  be  determined  by  chemical  analysis. 
By  the  determination  of  the  lowering  of  the  freezing-point  (cryoscopy) 
we  have  a  direct  means  of  accomplishing  our  end.  By  finding  out  the 
freezing-point  of  blood  and  of  urine  it  is  possible  to  discover  a  les- 
sened permeability  of  the  kidneys  for  dissolved  molecules  and  disturb- 
ances in  the  secretion  of  water. 

The  freezing-point  is  determined  by  Beckman's  differential  ther- 
mometer. Thus,  the  freezing-point  of  blood-scrum  of  mammals  is 


PHYSIOLOGY. 

0.5G°  C.  lower  than  water.  It  is  usually  expressed  by  the  Greek  delta 
(  A) .  A  solution  of  NaCl  of  0.95-per-cent.  strength  gives  the  same  A  ; 
hence  the  two  solutions  have  the  same  osmotic  pressure  and  0.95  per 
cent,  of  NaCI  is  isotonic  with  mammals'  serum.  The  osmotic  pressure 
of  urine  has  the  highest  isotonic  coefficient  of  any  fluid  in  the  body, 
and  its  A  is  equal  to  1.85°  C. 

The  most  important  electrolytes  present  in  blood-serum  are  the 
inorganic  salts  NaCI  and  Na2C03. 

The  freezing-point  of  defibrinated  blood  is  the  same  as  that  of 
serum;  in  other  words,  the  presence  of  blood-corpuscles  has  no  effect 
upon  the  freezing-point.  This  ensues  because  proteids  have  an  ex- 
ceedingly low  osmotic  pressure,  although  a  high  molecular  weight. 
The  freezing-point  of  blood  does  not  change  during  haemorrhage. 

In  metabolism  the  large  proteid  molecules  which  in  solution  exert 
an  exceedingly  low  osmotic  pressure  are  split  into  smaller  ones.  In 
consequence  the  number  of  dissolved  molecules  in  the  tissue  fluids  and 
in  the  blood  is  increased,  which  causes  an  increase  in  the  depression 
of  the  freezing-point  of  these  fluids.  The  loss  of  water  by  the  body 
through  evaporation  has  a  similar  effect.  It  is  the  function  of  the 
kidneys  to  rid  the  body  of  this  excessive  number  of  molecules  and  so 
keep  the  osmotic  pressure  of  the  blood  and  of  the  other  fluids  con- 
stant. If  the  activity  of  the  kidneys  is  decreased,  the  depression  of  the 
freezing-point  of  the  blood  will  become  greater.  A  beginning  renal 
insufficiency  will  therefore  be  manifested  by  an  abnormally  great  de- 
pression of  the  freezing-point  of  the  blood.  The  work  done  by  the 
secretory  cells  of  the  kidneys  in  secreting  the  urine,  the  osmotic  pres- 
sure of  which  is  much  higher  than  that  of  the  blood,  can  be  calculated 
by  utilizing  the  laws  of  osmotic  pressure.  If  the  kidne}rs  secrete  200 
cubic  centimeters  of  urine,  the  energy  required  amounts  to  37  kilo- 
grammeters;  that  is,  the  energy  required  is  equal  to  that  expended 
in  raising  a  weight  of  37  kilograms  to  the  height  of  1  meter.  The 
freezing-point  of  a  solution  of  any  substance  in  water  is  lower  than 
that  of  the  water  alone.  The  kidney-cells  separate  urine  from  the 
blood  against  a  pressure  of  a  force  about  six  times  greater  than  the 
maximum  force  of  muscle.  The  molecular  weight  of  a  body  can  be 
determined  by  the  depression  of  the  freezing-point. 

Another  theory  has  been  proposed  to  explain  the  low  freezing- 
point  of  urine.  Ludwig  proved  that  the  glomerulus  filters  a  nearly 
pure  solution  of  sodium  chloride  and  that  in  the  urinary  tubules  the 
water  is  in  part  reabsorbed.  The  theory  of  Koranyi  is  that  in  the 
urinary  tubules  there  is  a  molecular  exchange  in  such  a  manner  that  for 


ABSORPTION.  113 

each  molecule  of  urinary  constituents  coming  from  the  blood  there  is 
a  molecule  of  sodium  chloride  passing  from  the  tubules  into  the  blood. 

Loeb  has  shown  that  rhythmical  contractions  can  be  produced  at 
will  in  striped  muscles  of  the  frog  by  a  single  salt  solution.  This  is 
not  produced  by  the  salt  itself,  but  the  ions,  because  it  occurs  only  in 
solutions  of  electrolytes ;  that  is,  substances  which  dissociate.  Among 
the  ions  found  in  the  blood  he  thinks  those  of  sodium  are  the  pro- 
ducers of  rhythmical  activity.  Pure  sodium  chloride  he  regards  as  a 
poison.  If  rhythmical  activity  begun  by  it  is  to  persist,  these  poi- 
sonous properties  must  be  neutralized  by  calcium  salts.  Loeb  thinks 
calcium  and  potassium  salts  prevent  rhythmical  activity,  but  that  they 
in  conjunction  with  sodium  chloride  bring  about  a  sustained  rhythm. 
He  believes  the  sodium  ion  acts  by  migrating  into  the  muscle-substance 
and  combining  with  some  part  of  it.  Hence,  when  too  many  sodium 
ions  have  combined  and  taken  the  place  of  a  number  of  calcium  ions  in 
the  muscle,  rhythmical  beats  cease.  The  poisonous  effects  of  Na  ions 
are  antagonized  by  the  addition  of  a  small  amount  of  Ca  and  K  ions. 
Muscles  contract  only  as  long  as  they  contain  all  three  classes  of  ions 
(Na,  Ca,  and  K)  in  a  certain  proportion,  which  may  vary  to  a  certain 
extent. 

Numerous  substances  have  been  classified  on  the  basis  of  the 
degree  which  they  possess  of  passing  through  a  membrane  while  in 
aqueous  solution.  Those  which  pass  through  freely  have  been  found 
to  be  capable  of  crystallization  as  a  rule,  so  are  termed  crystalloids; 
those  which  are  more  tardy  in  their  osmosis  through  a  separating  mem- 
brane have  been  ascertained  to  be  noncrystallizable,  but  gluelike  in 
nature,  hence  are  known  as  colloids.  The  colloids  are  very  feeble  in 
all  chemical  relations,  the  reverse  being  true  of  the  crystalloids.  Ex- 
amples of  colloids  are  seen  in  albumins,  gelatin,  and  starch,  while 
alcohol,  sugar,  and  ordinary  saline  substances  form  good  examples 
of  crystalloids. 

Filtration. — Filtration,  synonymous  with  transudation,  is  the 
passage  of  fluid  or  fluids  through  the  pores  and  interstices  of  a  mem- 
brane while  subjected  to  pressure.  The  amount  of  filtration  is  pro- 
portional to  the  extent  and  quantity  of  pressure;  thus,  the  greater  the 
pressure,  the  greater  is  the  amount  of  fluid  made  to  pass  through  the 
separating  membrane.  The  rapidity  and  duration  of  filtration  is 
strongly  modified  by  the  nature  of  the  fluids  used  and  the  kinds  of 
membrane  through  which  the  various  fluids  are  made  to  pass  undor 
pressure.  Colloids  can  be  made  to  filter,  but  their  passage  is  much 
less  free  than  is  that  of  crystalloids.  In  the  pathological  condition 


114  PHYSIOLOGY. 

known  as  dropsy,  there  is  presented  a  partial  example  of  filtration.  It 
is  characterized  by  a  transudation  of  the  watery  portion  of  the  blood 
through  the  membranous  walls  of  the  capillaries  and  small  veins  into 
the  surrounding  connective  tissues,  producing  cedema.  This  watery 
element  has  been  literally  squeezed  through  the  vessel-walls  because 
of  increased  intravascular  pressure  within  the  capillaries  and  small 
veins.  The  causes  of  this  increased  pressure  are  numerous  and  need 
not  be  dealt  with  here. 

Loeb  explains  this  cedema  by  a  greater  osmotic  pressure  in  the 
tissues  than  in  the  blood  or  lymph.  Chemical  changes  in  the  muscle 
take  place  which  increase  the  osmotic  pressure.  These  chemical  con- 
ditions are  the  result  of  a  diminished  supply  of  oxygen  caused  by 
deficient  circulation. 

Rapidity  of  Absorption. — The  rapidity  of  absorption  has  been 
determined  by  experiment.  Thus  it  was  found  that  lithium  chloride 
may  be  diffused  throughout  all  of  the  vascular  structures  and  even 
into  some  of  the  nonvascular  ones,  as  the  cartilage  of  the  hip-joint  and 
aqueous  humor  of  the  eye,  within  a  quarter  of  an  hour  after  having 
been  given  on  an  empty  stomach.  When  lithium  carbonate  is  taken 
in  5-  or  10-grain  doses,  its  presence  may  be  detected  in  the  urine 
within  five  or  ten  minutes;  the  time  for  appearance  is  doubled  or 
even  trebled  when  the  substance  is  taken  on  a  full  stomach. 

It  is  interesting  as  well  as  curious  to  note  that  some  of  the  mineral 
and  vegetable  poisons  are  more  readily  absorbed  from  the  rectum  than 
the  stomach.  Thus,  it  has  been  ascertained  that  strychnine  in  solu- 
tion will  produce  toxic  effects  very  much  sooner  when  injected  into 
the  rectum  than  when  administered  by  the  stomach.  When  adminis- 
tered in  solid  form  the  reverse  is  true. 

THE  LYMPHATIC  SYSTEM. 

Having  previously  dwelt  upon  absorption  as  it  occurs  in  the 
alimentary  tract,  it  remains  to  turn  our  attention  to  the  next  important 
process  in  the  general  absorption  of  the  body.  It  is  the  absorption 
from  within  as  accomplished  by  the  lymphatic  system.  By  it  as  an  in- 
strument those  materials  of  the  alimentary  end-products  that  were  not 
taken  up  by  the  lacteals  are  collected  and  transported  back  into  the 
regular  blood-stream,  while,  on  the  other  hand,  fluid  which  has  escaped 
from  the  blood-vessels  and  has  not  been  used  by  the  tissues  is  gathered 
up  and  again  carried  back  into  the  blood-stream.  Very  frequently 
this  fluid  gathered  from  the  tissues  of  the  body  after  it  has  given  up 
much  of  its  nutriment  to  the  tissues  contains  numerous  bacteria, 


ABSORPTION.  115 

pathogenic  and  otherwise,  as  well  as  particles  of  waste-matter  from 
the  tissues.  These  are  normally  destroyed  by  the  lymphocytes ;  if  the 
foreign  particles  are  too  numerous  for  immediate  destruction,  they 
are  stored  up  in  the  lymphatic  glands,  or,  more  properly,  nodes,  until 
the  lymphocytes  are  able  to  dispose  of  them. 

The  watery  fluid  which  transudes  from  the  vessels,  particularly 
the  capillaries,  is  known  as  the  lymph.  It  is  this  fluid  which  bathes 
every  cell  of  all  the  tissues  to  give  them  nutriment,  while  it  carries 
away  from  these  same,  tissues  the  products  of  their  activity.  It  is  col- 
lected by  a  system  of  channels  and  vessels  which  unite  to  form  one 
main  trunk — the  thoracic  duct — and  a  second,  shorter  and  smaller 
duct,  and  both  empty  into  the  subclavian  veins:  the  thoracic  duct 
into  the  left  and  the  shorter  lymphatic  duct  into  the  right  subclavian. 
By  this  means  the  lymph  once  more  enters  the  blood-stream  to  be 
again  used  and  perform  perhaps  identical  functions.  The  vessels  with 
their  adnexa  which  convey  the  lymph  back  to  the  blood-stream  again 
comprise  a  system  known  as  the  lymphatic  system. 

Lymphatic  Vessels. 

In  order  to  nourish  the  tissues  of  the  body,  the  plasma  of  the 
blood  is  constantly  being  osmosed  through  the  capillary  walls  into 
spaces  between  the  cells  of  the  tissues.  Each  cell  is  thus  bathed  in  a 
plentiful  supply  of  plasma,  from  which  it  absorbs  what  is  needed  for 
its  nourishment.  This  escaped  blood-plasma,  together  with  some 
white  cells  which  have  found  their  way  into  the  spaces,  constitute 
the  lymph.  To  prevent  oedema  from  its  accumulation,  as  well  as  to 
have  it  with  its  contained  impurities  reach  the  blood  from  which  it 
may  be  excreted,  Nature  makes  use  of  a  set  of  tubes,  the  lymphatics. 
These  vessels  are  found  within  the  body  generally,  even  in  those  struc- 
tures which  contain  no  blood-vessels,  as  the  cornea  of  the  eye.  The 
fluid  within  them  always  moves  in  one  direction  only:  toward  the 
heart.  These  vessels,  whose  sources  may  be  very  different,  unite  in 
their  course  to  form  larger  vessels  until,  by  continual  union,  they 
terminate  in  two  large  trunks  which  empty  into  the  subclavian  veins 
at  their  junction  with  the  internal  jugulars.  The  one  emptying  into 
the  left  side  is  the  thoracic  duct,  that  into  the  right  side  is  the  right 

lymphatic  trunk. 

Structure   of  the   Lymphatics. 

When  the  agriculturist  wishes  to  drain  his  wet  lowlands  he  resorts 
to  the  use  of  pipes  of  great  porosity.  These  are  buried  and  so  arranged 
that  the  moisture  of  the  soil  very  readily  finds  its  way  into  the  pipes, 


116  PHYSIOLOGY. 

to  flow  along  them  and  so  be  conveyed  away.  When  the  arrangement 
of  the  pipes  is  suitable,,  the  excess  of  water  is  carried  off.  Should  the 
drain-pipes  become  defective,  or  should  their  capacity  be  less  than 
that  demanded  of  them,  there  at  once  results  a  stagnation  with  inun- 
dation of  the  land.  For  the  water  to  find  its  way  from  between  the 
particles  of  earth  and  sand  into  the  pipes  it  is  necessary  that  the  latter 
be  very  porous  and  permeable — a  most  essential  factor. 

The  principle  underlying  the  structure  of  the  lymphatics  is  very 
similar  to  that  of  the  system  of  drain-pipes  of  the  agriculturist, 
— namely:  porosity, — for  the  aim  of  each  is  to  collect  the  excess  of 
their  respective  fluids  and  convey  the  same  to  certain  desired  channels. 

This  principle  being  kept  in  mind,  the  student  can  readily  con- 
ceive the  nature  of  the  lymphatics. 

They  must  be  vessels  of  thin  walls — walls  which  allow  of  the 
easy  osmosis  of  plasma  through  them.  In  fact,  the  lymphatic  vessel- 
walls  are  similar  in  structure  to  those  of  veins,  differing  mainly  in 
the  fact  that  the  former  are  thinner.  Like  the  larger  veins,  the  larger 
lymphatics  consist  of  three  coats.  The  inner  is  made  of  endothelium 
(tunica  intima),  the  middle  coat  contains  some  muscular  fibers  (tunica 
media),  while  the  external  coat  is  connective  tissue  (tunica  adventitia) . 

The  small  lymphatics  have  walls  composed  of  but  a  single  layer 
of  endothelial  cells,  whose  edges  are  usually  sinuous.  So  thin  and 
translucent  are  the  walls  of  many  that  the  clear  tymph  contained  in 
them  can  be  clearly  defined. 

Like  some  veins,  the  larger  lymphatics  contain  valves  of  a  fibrous 
nature  lined  with  endothelium.  In  form,  structure,  and  attachments 
they  are  identical  with  those  of  the  veins.  Usually  two  valves  of  equal 
size  are  found  opposite  one  another ;  these,  by  their  functions,  prevent 
reflux  of  the  lymph  when  pressure  or  other  disturbance  is  brought  to 
bear  upon  their  course. 

Where  Nature  has  vessels  with  thin  walls  and  which  vessels  con- 
tain fluids  propelled  by  very  weak  vis  a  tergo,  she  must  needs  resort 
to  numerous  valves.  So  numerous  are  these  little  safeguards  that 
when  the  lymphatics  are  injected  they  present  the  appearance  of  a 
string  of  beads. 

While  dealing  with  lymphatics,  mention  must  be  made  of  those 
modified  lymphatics  known  from  ancient  times  as  the  lacteals.  These 
vessels  take  their  origin  from  the  intestines  to  empty  their  contents 
via  the  thoracic  duct  into  the  left  subclavian  vein  for  admixture  with 
the  systemic  blood.  The  lacteals  were  so  named  from  their  white 
color  at  certain  times;  that  is,  during  active  digestion,  when  the 


ABSORPTION.  H7 

lymph-stream  is  overwhelmed  by  the  absorbed  fatty  granules,  which 
give  to  it  its  milky  hue.  The  milky-colored  fluid  has  been  termed 
chyle.  During  the  intermission  between  active  digestion  the  lacteals 
carry  pure  lymph,  and,  from  their  functions  and  structure  being 
identical  with  that  of  true  lymphatics,  they  deserve  to  be  classed  with 
the  latter. 

Origin  of  the  Lymphatics. 

Though  many  features  of  this  system  are  yet  obscure  and  open 
for  investigation,  it  seems  very  probable  that,  as  stated  by  Landois, 
the  lymphatics  arise  as  follows: — 

1.  Connective-Tissue   Spaces. — These   are   very   numerous,   star- 
shaped  or  irregularly  branched  spaces  which  communicate  with  one 
another  by  fine  tubular  processes.     They  are  lined  with  endothelium 
and  contain  lymph  and  a  few  "wandering  cells." 

2.  Within  the  Villi. — This  mode  has  been  discussed  under  the 
subject  of  "Digestion." 

3.  In  Perivascular  Spaces. — The  small  blood-vessels  which  supply 
bone,   central   nervous   tissue,   retina,   and   the  liver   are  themselves 
surrounded  by  lymphatic  tubes  which  in  many  instances  are  larger 
than  the  blood-vessels.     Between  these  tubes   and  the  blood-vessels 
there  exists  a  space  called  the  perivascular  space  of  His.     These  are 
believed  to  be  one  source  of  lymphatics,  for,  when  they  exist,  the 
passage   of   lymph-corpuscles   into   the   lymphatic   vessels   is   greatly 
facilitated. 

4.  In  the  Form  of  Interstitial  Slits  Within  Organs.— Within  the 
testicle  and  certain  other  organs  there  exist  long,  slitlike  spaces  between 
the  various  cells  and  network  of  tubules.     They  are  all,  however,  lined 
with  endothelium.     Into  these  spaces  there  is  poured  lymph  from  the 
blood-capillaries  for  the  maintenance  of  the  glandular  cells,  and  at 
the  same  time  it  furnishes  material  for  secretion.     From  these  little 
slits  lymphatics  take  their  origin,  but  receive  independent  walls  after 
their  exit  from 'the  gland -substance. 

5.  By  Means  of  Free  Stomata. — These  occur,  for  the  most  part, 
upon  the  walls  of  the  larger  serous  cavities.     Lymph  is  pumped  here 
by  the  alternate  dilatation  and  contraction  of  the  serous  surface,  due 
to  the  movements  of  respiration  and  circulation;   so  that  serous  sacs 
may  be  regarded  in  a  certain  sense  as  large  lymph-cavities.     Fluids 
placed  within  these  cavities  readily  find  their  way  into  the  lymphatics. 
The  cavities  referred  to  are  those  of  the  peritoneum,  pleura,  peri- 
cardium, aqueous  chamber  of  the  eye,  and  labyrinth  of  the  ear. 


118  PHYSIOLOGY. 

6.  In  the  mucous  membrane  of  the  nose,  larynx,  trachea,  and 
bronchi  there  have  been  noticed  open  pores  which  are  in  communica- 
tion with  the  lymphatics. 

Lymphatic  vessels  of  moderate  size  are  supplied  with  nutrient 
vessels  (vasa  vasorum),  which  are  distributed  to  the  external  and 
middle  coats  of  their  walls;  up  to  the  present  time  no  nerve-supply 
has  as  yet  been  ascertained  except  for  the  thoracic  duct. 

Lymphatic  glands  are  hard,  pinkish  bodies  varying  in  size,  and 
are  principally  ovoidal.  They  are  generally  situated  along  the  course 
of  the  larger  blood-vessels.  The  afferent  vessels  enter  the  gland  at 
various  points  on  its  surface.  The  efferent  vessels  emerge  from  a 
slight  concavity  on  one  side  of  the  gland  called  the  hilum.  In  this 
hilum  the  blood-vessels  course.  There  are  two  parts  in  a  lymphatic 
gland:  the  outer,  lighter  part,  called  the  cortex;  and  the  darker 
interior,  called  the  medulla. 

A  fibrous  covering  envelops  the  lymph-gland  and  sends  partitions 
into  the  gland,  cutting  it  up  into  spaces  called  alveoli.  These  alveoli 
communicate  freely  with  each  other,  and  are  filled  with  a  lymphoid 
tissue  where  the  leucocytes  are  undergoing  division.  They  are  genera- 
tors of  lymphocytes. 

Flow  of  Lymph  and  Chyle. 

The  lymph  and  chyle  always  run  in  a  centripetal  direction  from 
the  periphery  to  the  center  under  the  influence  of  various  forces. 
The  villi  contract  and  push  their  contents  in  a  centripetal  course, 
aided  by  the  contractions  of  the  intestinal  muscles.  The  dilatation 
of  the  blood-vessels  at  each  contraction  of  the  heart  pushes  the  lymph 
out  of  the  perivascular  spaces.  Although  the  lymphatic  cells  by 
their  proper  activity  are  the  principal  cause  of  the  passage  of  the 
plasma  from  the  blood-vessels  into  the  lymphatic  capillaries,  yet  it  is 
necessary  to  admit  that  the  arterial  blood-pressure  contributes  in  a 
marked  manner.  By  this  exudation  the  interstitial  pressure  always 
tends  to  the  same  height  as  the  intracapillary  pressure — the  stronger 
the  intracapillary  pressure,  the  stronger  the  interstitial  pressure.  On 
the  other  hand,  the  stronger  the  interstitial  pressure,  the  more  easily 
the  lymph  will  be  absorbed  by  the  lymphatic  capillaries.  We  must 
admit  with  Ludwig  that  the  pressure  of  the  blood  is  a  powerful  cause 
in  the  circulation  of  the  lymph,  and  this  can  be  easily  shown  by  sec- 
tion and  irritation  of  the  spinal  cord,  after  a  cannula  has  been  intro- 
duced into  the  thoracic  duct,  where  the  lymph-flow  decreases  with  the 
dilatation  of  blood-vessels  on  section  of  the  cord  and  increases  on  irri- 


ABSORPTION.  H9 

tation  of  the  cut  section.  Once  the  lymph  and  chyle  are  in  the 
vessels  it  continues  to  move  by  the  muscular  contraction  of  the  walls  of 
these  vessels,  and  this  movement  can  only  take  place  in  a  centripetal 
direction  by  reason  of  the  arrangement  of  the  valves.  The  lymphatic 
ganglia,  by  their  structure,  offer  a  resistance  to  the  circulation  of  the 
lymph,  but  their  fibrous  covering  and  unstriped  muscles  favor  the 
flow.  Cold-blooded  animals  have  lymphatic  hearts  which  act  as  motors 
in  circulating  the  lymph.  The  valves  in  the  lymphatic  vessels  are 
powerful  adjuvants  in  propelling  the  lymph  in  a  central  direction. 
The  respiratory  movements  have  an  influence.  At  the  time  of  inspira- 
tion the  flow  of  lymph,  like  the  blood,  rushes  into  the  chest,  owing 
to  the  partial  vacuum  in  the  chest.  The  pressure  by  muscular  action 
on  the  lymphatics  also  greatly  aids  in  the  propulsion  of  the  lymph. 

Lymph  moves  at  the  rate  of  about  ten  inches  per  minute,  and  its 
pressure  is  fifteen  millimeters  of  soda  solution. 

The  nervous  system  bears  a  direct  relation  to  the  lymph-stream 
in  so  far  as  it  governs  the  musculature  of  the  lymph-trunks  and 
capsule  and  trabeculae  of  the  lymph-glands.  A  solution  of  common 
salt  injected  beneath  the  skin  of  a  frog  will  be  rapidly  absorbed,  unless 
the  central  nervous  system  be  destroyed,  when  no  absorption  takes 

place. 

Composition  of  the  Lymph. 

Lymph  is  an  albuminous,  colorless  fluid  which  contains  lymph- 
corpuscles;  these  are  identical  with  the  colorless  blood-corpuscles. 
Lymph  is  alkaline,  has  a  specific  gravity  of  about  1.015,  and  when 
drawn  from  its  vessels  it  clots,  forming  a  colorless  coagulum  of  fibrin. 
The  watery  part  of  the  lymph  is  known  as  the  lymph-plasma,  which 
contains  the  three  elements  necessary  for  coagulation:  fibrinogen, 
fibrin-ferment,  and  calcium  salts.  It  is  very  similar  to  blood-plasma, 
only  diluted  so  far  as  its  proteid  constituents  are  concerned.  The 
proteids  present  are  fibrinogen,  serum- globulin,  and  serum-albumin. 
The  salts  contained  in  solution  are  present  in  smaller  proportion  than 
those  found  in  blood-plasma.  The  waste-products — urea,  carbonic 
acid,  leucin,  etc. — are  more  abundant  in  the  lymph  than  in  blood; 
the  solids  herein  contained  reach  4  per  cent.,  of  which  3  Y2  per  cent, 
are  proteid  in  nature.  The  amount  of  glucose  is  about  the  same  as 
in  blood-plasma.  The  lymphocytes  contain  glycogen. 

The  apparently  transparent  lymph  is  found  to  contain  corpuscles 
when  examined  under  the  microscope;  to  them  the  name  lymphocytes 
has  been  applied.  They  have  a  large  nucleus  with  comparatively  little 
protoplasm.  In  some  places — the  thoracic  duct,  for  example — a  few 


120  PHYSIOLOGY. 

colored  blood-corpuscles  are  found  and  are  believed  to  have  found 
their  way  into  this  distinct  system  by  reason  of  diapedesis.  The 
regular  lymphocytes  find  their  way  into  the  blood-stream,  where  they 
multiply  and  are  known  as  leucocytes. 

The  real  manufactories  of  these  lymphocytes  are  the  lymphatic 
glands,  whose  alveoli  contain  adenoid  tissue.  The  number  of  lym- 
phocytes is  much  greater  in  the  lymph  after  it  has  passed  through  a 
gland,  and  we  find  that  lymph  collected  from  regions  where  there  are 
few  glands,  as  the  lower  extremities,  is  always  poorer  in  albumin  and 
richer  in  water  than  the  lymph  in  the  large  lymphatic  vessels. 

For  purposes  of  analysis,  lymph  can  be  obtained  from  the  limbs, 
thoracic  duct,  and  serous  cavities.  Accidental  lymphatic  fistulse  in 
man  as  well  as  experimental  ones  in  animals  have  been  the  source  of 
much  lymph  for  analytical  purposes. 

The  pericardial  fluid  and  aqueous  humor  are  forms  of  lymph 
which  are  not  coagulable  except  upon  the  addition  of  fibrin-ferment. 
Cerebro-spinal  fluid  has  the  identical  appearance  of  lymph,  but  differs 
from  it  in  chemical  properties  and  composition. 

Synovial  fluid  of  joints  differs  from  true  lymph  in  that  it  contains 
mucin  or  mucinlike  bodies  and  a  high  percentage  of  solids. 

Chyle  is  the  term  used  to  designate  the  fluid  of  the  lacteal  system 
during  active  digestion,  particularly  of  fats.  It  is  an  opaque,  whitish, 
milky  fluid,  neutral  or  slightly  alkaline  in  reaction.  The  color  of  the 
chyle  is  due  to  the  presence  in  it  of  numerous  fatty  granules,  each 
surrounded  by  an  albuminous  envelope,  very  minute,  though  uniform 
in  size.  Their  fatty  nature  becomes  evident  when  they  are  treated 
with  ether,  for  they  are  immediately  dissolved.  Varying  quantities 
of  the  fat  give  different  shades  of  whiteness  to  the  chyle.  Thus,  in 
addition  to  the  constituents  of  the  lymph,  the  chyle  contains  a  large 
amount  of  fat,  which  is  its  characteristic  feature.  During  fasting  the 
chyle  in  the  lacteals  resembles  ordinary  lymph. 

As  the  chyle  passes  on  toward  the  thoracic  duct,  especialty  when 
traversing  some  of  the  mesenteric  glands,  it  is  elaborated.  As  a  result 
there  are  fewer  fat-particles,  but  there  now  begin  to  appear  corpuscles 
to  which  the  name  chyle-corpuscles  is  applied.  Further,  it  now  gains 
the  ability  to  coagulate  spontaneously.  As  the  chyle  advances  in  the 
thoracic  duct  the  corpuscles  become  more  numerous,  and  the  larger 
and  firmer  becomes  the  clot  when  the  chyle  is  withdrawn  from  its 
vessels.  The  clot  is  like  that  of  blood  when  only  white  corpuscles  are 
present.  Its  ability  to  coagulate  is  due  to  the  disintegration  of  the 
lymph-corpuscles  which  supply  it  with  the  necessary  fibrin-factors. 


ABSORPTION.  121 

Quantity  of  Lymph  and  Chyle. 

It  may  be  roughly  stated  that  the  amount  of  lymph  and  chyle 
combined  passing  through  the  large  vessels  in  twenty-four  hours  is 
about  twelve  pounds.  The  formation  of  lymph  in  the  tissues  takes 
place  continually  and  without  interruption. 

It  must  be  remembered  that  the  total  quantity  of  the  lymph  and 
chyle  is  not  a  constant  factor,  but  may  become  affected  by  different 
conditions.  Thus,  the  amount  of  chyle  becomes  very  much  increased 
during  digestion;  is  diminished  during  hunger.  The  amount  of 
lymph  increases  with  the  activity  of  the  organ  from  which  it  proceeds, 
while  active  or  even  passive  movements  of  the  muscles  greatly  increase 
its  amount.  Conditions  which  increase  the  pressure  of  the  vascular 
supply  of  the  tissues  increase  the  amount  of  lymph,  and  vice  versa. 

Formation  of   Lymph. 

Ludwig  thought  the  lymph  was  regulated  by  differences  between 
the  arterial  tension  and  the  interstitial  pressure,  and  to  chemical  dif- 
ferences between  the  two  liquids  resulting  in  an  osmosis  through  the 
wall  of  the  blood-vessel.  Heidenhain  has  sought  to  prove  that  the 
lymph  is  a  true  secretory  product.  The  quantity  and  composition  of 
this  liquid  was  regulated  by  the  elective  activity  of  the  cells  of  the 
capillaries.  He  considers  the  force  developed  by  the  cells  as  one  of 
the  principal  causes  of  the  flow  of  the  lymph.  He  based  his  con- 
clusions on  the  fact  that  the  quantity  of  lymph  produced  is  not  always 
exactly  parallel  in  the  value  of  the  arterial  tension.  Lymph  can 
flow  for  many  hours  after  death  when  a  fistula  has  been  made  in  the 
thoracic  duct.  He  also  found  that  certain  substances,  as  glucose, 
is  larger  in  amount  in  the  lymph  than  the  blood,  due,  as  he  believes, 
to  the  selective  action  of  the  endothelial  cells  of  the  lymphatics. 

Heidenhain  makes  two  classes  of  lymphagogues.  In  his  first  class 
a  decoction  of  crayfish,  leeches,  or  mussels  in  the  blood  increases  the 
flow  of  lymph  from  the  thoracic  duct,  acting  upon  the  endothelial 
cells  of  the  capillaries.  They  cause  a  slight  injury  to  the  capillary 
wall,  thus  increasing  its  permeability,  so  that  a  slight  rise  of  pressure 
greatly  increases  the  transudation.  They  chiefly  affect  the  capillaries 
of  the  liver.  Curare  has  a  specific  action  on  the  endothelial  cells  of 
the  capillaries,  causing  an  increase  of  lymph.  The  second  class  of 
lymphagogues — like  sugar,  salt,  potassium  iodide,  and  peptone — 
abstract  water  from  the  tissues  into  the  blood,  thus  raising  arterial 
tension  and  increasing  the  flow  of  lymph. 


122  PHYSIOLOGY. 

Skin  and  Lungs. 

It  remains  to  consider  the  nature  of  the  absorption  that  takes 
place  through  the  skin  and  lungs.  These  avenues  are  but  subsidiary 
ones  to  the  two  greater  ones  just  mentioned:  intestinal  absorption 
and  that  along  the  lymphatic  system.  Absorption  through  one  of 
them  takes  place  from  without;  so  that  it  is  usually  classed  with  the 
first  of  the  two  processes  of  absorption  mentioned  at  the  beginning  of 
this  chapter. 

For  a  long  time  it  was  a  subject  for  much  discussion  whether 
water  was  absorbed  by  the  skin  with  the  epidermis  still  intact.  It 
was  a  rather  difficult  matter  to  ascertain,  since  the  skin  is  constantly 
giving  off  water  in  the  form  of  perspiration,  sensible  or  insensible. 
The  absorption  of  water  through  the  skin  covering  the  body  takes 
place  very  rapidly  in  the  lower  animals.  It  has  been  finally  ascer- 
tained that  absorption  of  water  does  take  place  through  the  skin  of 
man,  but  to  a  much  less  degree  than  occurs  in  animals.  Aqueous  solu- 
tions of  various  drugs  when  in  simple  contact  with  the  skin  are  only 
slightly  active.  It  is  believed  that  the  great  hindrance  to  their  ab- 
sorption is  the  presence  of  the  fat  that  is  normally  present  upon  the 
skin  and  in  its  pores  and  interstices.  If  this  be  removed  by  the  appli- 
cation of  alcohol,  ether,  or  chloroform,  physiological  effects  of  the 
drugs  are  soon  manifested. 

Inunction. — When  ointments  are  rubbed  into  the  skin  so  as  to 
press  the  substance  in,  absorption  will  take  place.  Mercury  when 
applied  in  this  manner  exerts  its  specific  effect  upon  syphilis  and  ex- 
cites salivation ;  tartar  emetic  so  applied  may  produce  vomiting  or  an 
eruption  extending  over  the  entire  body.  Voit  found  globules  of  mer- 
cury between  the  layers  of  the  epidermis  and  even  in  the  corium  of  a 
person  who  had  been  executed  and  into  whose  skin  mercurial  ointment 
had  previously  been  rubbed.  An  abraded  or  inflamed  surface  absorbs 
very  rapidly. 

Under  normal  conditions  minute  traces  of  0  are  absorbed  from  the 
air;  CO,  C02,  vapor  of  chloroform,  and  ether  may  also  be  absorbed. 

In  dysphagia,  when  the  condition  is  •  so  severe  that  even  fluids 
cannot  be  taken  into  the  stomach,  immersion  of  the  patient  into  a 
bath  of  warm  water  or  water  and  milk  may  quench  the  thirst.  It 
is  well  known  that  sailors,  when  destitute  of  fresh  water,  assuage 
their  thirst  by  wetting  their  clothing  with  salt  water  and  wearing 
them  until  dry.  It  is  very  probable  that  the  effects  produced  are  in 
a  great  measure  attributed  to  hindrance  to  the  evaporation  of  water 
from  the  skin. 


ABSORPTION.  103 

Through  the  Lungs. — It  is  interesting  to  note  that  not  only  do 
gases  pass  through  the  epithelium  of  the  pulmonary  air-vesicles,  but 
that  fluids,  such  as  water,  may  be  absorbed  when  they  have  found  their 
way  into  the  air-passages.  The  presence  of  particles  of  carbon  in  the 
bronchial  glands  and  other  tissues  of  the  respiratory  apparatus  is 
accounted  for  only  by  reason  of  the  open  pores :  one  of  the  origins  of 
the  lymphatic  system. 


CHAPTER  V. 

THE    BLOOD. 

BLOOD  is  a  red,  somewhat  viscid  fluid,  denser  than  water,  and 
apparently  composed  of  but  one  substance.  This  liquid,  which  is 
usually  spoken  of  as  the  nutritive  fluid  of  the  body,  serves  as  an  in- 
ternal medium  of  exchange  existing  between  the  foodstuffs  found 
in  the  outer  world  and  the  cells  composing  the  various  tissues  of  the 
body.  It  was  constantly  kept  before  the  student's  attention  that  the 
main  and  ultimate  end  of  digestion  was  the  absorption  of  the  food- 
stuffs into  the  blood-stream,  not  as  proteoses  and  peptones,  but  as 
native  albumins  and  globulins — these  latter  the  results  of  the  living, 
vital  activity  of  the  epithelial  cells  of  the  villi  through  which  pass 
the  proteoses  and  peptones.  Thus,  into  the  blood  are  poured  new 
products  (the  work  of  digestion),  which  are  carried  by  its  circulation 
to  all  parts  of  the  body,  to  be  given  up  to  the  various  tissues  having 
need  of  them.  By  this  means  every  cell  receives  the  nutriment  neces- 
sary for  carrying  on  its  own  metabolic  processes,  either  directly  or 
indirectly.  For  the  student  will  remember  that  each  cell  possesses 
an  inherent  selective  capability.  From  the  pabulum  contained  in  the 
enveloping  lymph  it  is  able  to  take  up  those  factors  which  it  can 
work  up  into  its  own  constitution  to  form  an  integral  part  of  itself. 
These  constituents,  having  served  their  respective  purposes,  are  no 
longer  of  any  value  to  the  cell — they  are  waste-products,  and  as  such 
must  be  gotten  rid  of.  Passing  out  from  the  cell-substance,  they  find 
themselves  in  the  same  enveloping  lymph,  to  be  eventually  carried 
again  into  the  blood-stream  for  elimination  through  the  excretory 
activities  of  the  lungs,  kidneys,  and  skin.  Thus,  indirectly  the  blood 
is  a  medium  of  elimination  of  such  deleterious  products  as  urea,  uric 
acid,  water,  carbon  dioxide,  etc. 

However,  the  afferent  function  of  the  blood  is  not  simply  single, 
for  it  conveys  to  the  tissues  in  addition  that  material,  all-important 
for  successful  combustion, — namely,  oxygen, — which  has  been  ob- 
tained from  the  respired  air  of  the  lungs.  Among  warm-blooded 
animals  another  office  served  by  the  blood  is  to  equalize  to  a  certain 
degree  the  temperature  of  the  body. 
(124) 


THE  BLOOD. 


125 


Color. — There  are  certain  characteristics  which  distinctly  mark- 
blood  from  other  fluids.  The  color  of  the  blood  of  vertebrata  is  gen- 
erally red.  •  Its  shade  is,  however,  not  fixed.  As  the  blood-stream 
passes  through  a  variety  of  tissues  and  is  subjected  to  many  different 
conditions,  its  color  varies  from  a  scarlet  red  in  the  arteries  to  a 
bluish  red  found  within  the  veins.  It  is  the  presence  of  the  oxygen 
in  combination  with  hemoglobin  that  gives  to  the  arterial  blood  its 
bright  color.  Lessened  oxygen  means  excess  of  carbon  dioxide,  and 
it  is  the  presence  of  the  latter  which  gives  to  venous  blood  its  char- 
acteristic bluish-red  color. 

When  normal  blood  is  drawn  from  a  blood-vessel  to  be  placed 
upon  a  glass  slide  as  a  very  thin  film,  it  is  found  to  be  opaque,  and 
printed  matter  cannot  be  read  through  it.  This  opacity  is  produced 
by  differences  of  refraction  possessed  by  its  several  components.  The 
healthy  red  color  of  the  nails,  conjunctiva,  lips,  ears,  and  mucous 
membranes  in  general  is  due  to  the  presence  of  the  blood.  When 
there  is  insufficient  supply  to  these  parts, — temporarily  in  fainting  or 
for  a  longer  period,  as  in  ansemia, — they  become  pale  and  waxy  in  color. 
In  asphyxia  and  certain  heart  affections  there  is  a  want  of  proper 
oxidation,  with  a  resultant  bluish  color  to  the  above-named  parts. 

Reaction. — The  reaction  of  blood  is  alkaline.  This  alkalinity  is 
variable  in  amount.  Thus,  it  is  diminished  after  great  muscular  ex- 
ertion, owing  to  the  formation  and  presence  in  it  of  a  large  quantity 
of  sarco-lactic  acid.  After  long-continued  ingestion  of  soda  the  alka- 
linity is  increased;  after  the  use  of  acids  it  is  diminished.  In  no 
case,  however,  does  it  become  distinctly  acid.  To  test  the  alkalinity 
of  the  blood,  dry,  faintly  reddened  glazed  litmus-paper  is  used.  Upon 
it  is  placed  a  drop  of  blood,  which  is  allowed  to  remain  for  half  a 
minute,  to  be  then  wiped  off  with  a  weak  salt  solution.  The  result 
is  a  blue  spot  upon  a  red  background. 

Blood  possesses  a  distinctly  salty  taste.  It  owes  this  property 
to  the  presence  of  disodic  phosphate  and  bicarbonate  of  soda. 

Specific  Gravity. — The  specific  gravity  of  normal,  healthy  blood 
varies  within  certain  limits:  for  men,  about  1.057  to  1.066;  for 
women,  1.054  to  1.061.  Its  density  is  influenced  by  various  factors 
and  conditions.  If  fluids  be  used  sparingly  and  a  dry  diet  eaten,  the 
density  is  increased.  It  is  also  increased  by  exercise  and  profuse 
, sweating.  It  falls  when  fluid  is  injected  into  the  vessels,  but  for  a 
short  time  only. 

The  temperature  of  the  blood  varies  between  97.7°  and  100°  F. 
The  cutaneous  blood-supply  is  slightly  lower  in  temperature,  while 


126  PHYSIOLOGY. 

the  warmest  blood  is  that  in  the  hepatic  vein;  the  coldest  in  the  tip 
of  the  nose. 

Fresh  blood  imparts  a  decided  odor,  peculiar  to  the  animal  from 
which  it  is  drawn.  The  odor  of  blood  is  due  to  volatile  fatty  acids 
held  in  solution.  The  effect  becomes  more  striking  upon  the  addition 
of  concentrated  sulphuric  acid  to  the  blood. 

Quantity  of  Blood. — From  very  early  times  the  theme  of  the 
quantity  of  blood  circulating  within  the  body  has  been  uppermost  in 
the  minds  of  physiologists  and  investigators.  By  reason  of  the 
methods  then  employed  the  results  were  inaccurate  and  difficult  of  at- 
tainment. Simple  bleeding  was  resorted  to,  but  deductions  depended 
upon  the  rapidity  with  which  the  blood  was  lost.  If  the  animal  were 
bled  very  rapidly,  then  considerable  of  blood  remained  in  the  vessels. 
If  the  blood  was  extracted  very  slowly,  not  only  blood,  but  serum  from 
the  lymphatic  vessels,  spaces,  and  glands  was  obtained.  These  factors 
very  materially  altered  the  calculations. 

The  accepted,  though  not  very  simple,  method,  for  determina- 
tion of  quantity  is  that  of  Welcker's.  It  is  as  follows :  The  specific 
gravity  of  the  blood  as  well  as  weight  of  the  animal  are  first  noted. 
A  cannula  is  placed  in  the  animal's  carotid  through  which  is  extracted 
a  quantity  of  blood  to  serve  as  a  sample.  This  is  defibrinated,  where- 
upon portions  of  it  are  diluted  at  different  known  strengths.  The 
remainder  of  the  blood  in  the  body  is  then  allowed  to  escape,  and  is 
collected  and  defibrinated.  A  normal  salt  solution  is  next  run 
through  the  vessels  and  likewise  collected.  The  entire  body,  minus 
the  stomach  and  intestines,  is  then  cut  into  very  fine  pieces  and 
extracted  with  water  for  one  or  two  days,  at  the  end  of  which  time 
the  bloody  water  is  expressed  and  added  to  the  drawn  blood  and 
washings.  The  entire  amount  is  carefully  measured. 

The  experimenter  compares  this  diluted  blood  with  the  pre- 
'viously  prepared  samples  of  the  diluted  blood  of  known  strength  until 
he  finds  tints  of  two  that  are  exactly  alike.  From  the  total  quantity 
of  diluted  blood  and  the  knowledge  of  what  the  sample  contains  it  is 
comparatively  easy  to  calculate  the  amount  of  blood  contained  in  the 
body.  To  this  must  be  added  the  blood  drawn  at  first  to  make  the 
various  samples.  The  weight  of  the  animal  compared  with  the  above 
results  gives  the  proportionate  amount. 

By  this  and  similar  computations  it  has  been  ascertained  that 
the  blood  is  equal  to  from  one-eleventh  to  one-fourteenth  of  the 
body-weight.  Approximately,  it  may  be  said  to  be  one-thirteenth 
of  the  body-weight. 


THE  BLOOD.  jo? 

"Roughly,  it  may  be  said  that  the  lungs,  heart,  large  arteries, 
and  veins  contain  one-fourth ;  the  muscles  of  the  skeleton  one-fourth ; 
the  liver  one-fourth;  and  other  organs  one-fourth/'  (Eanke.) 

Arterial  and  Venous  Blood  Compared. — At  this  point  the  stu- 
dent's attention  is  called  to  but  a  few  main  points  wherein  the  arte- 
rial and  venous  bloods  differ.  Very  conspicuously  stands  out  the 
marked  difference  in  color:  the  scarlet  of  arterial,  the  bluish  red  of 
venous  blood.  These  color-differences  depend  primarily  upon  the 
amount  of  oxygen-gas  contained  in  the  blood.  It  unites  with  the 
iron  of  the  blood-corpuscles  (little  bodies)  to  form  a  very  unstable 
compound,  known  as  oxyhaemoglobin.  When  carbon-dioxide  gas  is 
present  it  also  forms  an  unstable  compound.  Its  color  is  dark.  When 
oxyhaamoglobin  is  in  excess,  as  it  is  in  arterial  blood,  the  color  is  a 
bright  red.  When  carbon  dioxide  is  in  the  ascendancy,  the  blood  is 
bluish  red  and  the  oxygen-gas  is  present  in  diminished  amounts. 

Arterial  blood  contains  more  of  the  assimilable  products  of  the 
digestive  processes,  so  that  it  is  better  fitted  to  supply  the  cells  with 
their  proper  nutrition  and  materials  to  the  various  glands  for  their 
secretions.  .  It  also  contains  greater  quantities  of  salts,  fats,  and 
sugars.  Venous  blood  contains  less  nutriment,  but  more  waste-prod- 
ucts resulting  from  catabolic  processes,  particularly  urea  and  carbonic 
acid. 

Composition  of  the  Blood.  —  Apparently  the  blood-stream,  as 
viewed  by  the  naked  eye,  is  composed  of  one  homogeneous,  red  sub- 
stance; but  when  examined  histologically  with  the  microscope  this 
impression  becomes  entirely  dispelled.  It  is  then  found  to  be  com- 
posed in  reality  of  a  transparent  liquid  portion,  known  as  the  plasma, 
or  liquor  sanguinis,  in  which,  as  a  medium,  float  an  immense  number 
of  Uood-corpuscles.  The  great  majority  of  these  latter  are  colored, 
and  it  is  due  to  them  that  the  blood  owes  its  color.  There  are  at 
least  three  different  kinds  of  blood-corpuscles,  commonly  known  as 
the  red  corpuscles;  the  white  corpuscles,  or  leucocytes;  and,  last, 
blood-plates. 

The  red  corpuscles  of  mammalia — the  camel  and  others  of  the 
group  of  CamelidcB  alone  being  excepted — are  circular  plates,  bicon- 
cave, and  without  nuclei.  Those  of  the  camel,  birds,  and  reptiles  are 
elliptical  and  biconvex. 

Human  red  blood-corpuscles  are  biconcave,  disc-shaped  bodies 
with  rounded  edges  and  slight  central  depressions.  They  have  been 
tersely  described  by  one  author  as  "circular,  biconcave,  nonnucleated 
discs." 


128  PHYSIOLOGY. 

The  corpuscles  are  formed  of  a  semisolid,  homogeneous,  iron- 
holding  mass  which  appears  to  have  no  membrane  or  nucleus,  for  a 
nucleus  is  normally  met  with  in  them  only  during  embryonic  life  of 
mammals  and  in  the  blood  of  the  lower  vertebrates,  as  the  amphibia. 
In  size,  they  are  about  1/320o  incn  in  diameter  and  1/120oo  incn  in  thick- 
ness. Various  causes  and  conditions  may,  however,  slightly  increase 
or  decrease  their  size. 


Fig.  15. — Blood-corpuscles  of  Different  Animals.     (THANIIOFFEE.) 

1,  Proteus.  2,  Rana  esculenta:  a,  upper  view  of  same;  6,  white  blood- 
corpuscles;  c,  side-view  of  red  corpuscles.  3,  Triton.  4,  Snake.  5,  Camel. 
6,  Turtle.  7,  Salamander.  8,  Carp.  9,  CoUtis  fossilte.  10,  Cuckoo.  11, 
Chicken.  12,  Canary  bird.  13,  Lion.  14,  Elephant.  15,  Man:  a,  upper  view 
of  same;  b,  crenated  form;  c,  white  blood-corpuscles.  16,  Horse's  cells  in 
rouleaux.  17,  Hippopotamus. 

Because  of  their  extremely  small  size  the  corpuscles  are  not 
really  red  when  viewed  singly  with  the  microscope,  but  rather  of  a 
pale  yellow  or  even  greenish  tinge.  It  is  only  when  millions  of  them 
are  en  masse  that  the  characteristic  red  color  becomes  apparent: 
scarlet  red  in  arterial  blood,  purplish  red  in  venous  blood.  These 
shades  of  red  are  occasioned  by  the  varying  proportion  of  oxygen  in 
combination  with  the  haemoglobin,  with  which  the  gas  unites  very 
readily.  Because  of  this  fact  it  falls  to  the  lot  of  these  little  bodies 
to  perform  a  very  important  function  for  the  economy,  viz. :  to  con- 


THE  BLOOD. 


129 


vey  oxygen  from  the  lungs  to  the  tissues  to  be  distributed  to  them. 
The  0  is  held  by  the  ha&moglobin  so  lightly  and  unstable  that  it  can 
be  very  readily  extracted  from  the  corpuscles  by  the  cells  of  the  tis- 
sues. Upon  the  blood  depends  the  internal  respiration  of  the  tissues 
and  all  oxidation  processes.  While  there  is  undoubted  active  oxida- 
tion occurring  in  the  blood  itself,  yet  the  blood  is  not  the  place  of 
the  oxidation  in  the  body.  The  cause  is  in  the  living  cells  of  the 
tissues.  In  addition  to  an  inherent  affinity  possessed  by  the  tissues 
for  oxygen,  its  passage  from  the  blood  to  the  tissue-cells,  as  also  the 
passage  of  carbon  dioxide  from  the  cells  back  to  the  blood-stream, 


B 


Fig.  16. — Human  and  Amphibian  Blood-corpuscles.     (LANBOIS.) 

A,  Human  red  blood-corpuscles:  1,  on  the  flat;  2,  on  the  edge;  3,  rouleaux 
of  red  corpuscles.  B,  Amphibian  red  corpuscle:  1,  on  the  flat;  2,  on  edge. 
C,  Ideal  transverse  section  of  a  human  red  corpuscle,  magnified  5000  times. 
a-b,  linear  diameter;  c-d,  thickness. 

depend  very  materially  upon  differences  of  pressure  of  these  two 
gases  in  the  blood  and  tissues.  The  direction  is  always  from  a  higher 
pressure  to  a  lower  one. 

A  peculiar  inherent  power  and  property  of  red  corpuscles  is  to 
arrange  themselves,  when  withdrawn  from  their  retaining  vessels,  in 
the  form  of  rolls  of  coin,  adhering  to  one  another  by  some  peculiar 
affinity.  To  describe  this  condition  the  term  rouleaux  has  been  used. 
This  peculiarity  becomes  particularly  marked  when  there  is  an  in- 
flammatory state  of  the  system.  Formation  of  rouleaux  can  be  pre- 
vented by  the  injection  of  physiological  saline  solution. 

Parasites  of  Blood-corpuscles. — In  the  red  corpuscles  of  some 
birds  and  fishes  the  microscopist  frequently  notices  small,  transparent 


130  PHYSIOLOGY. 

spots.  These  are  "  pseudovacuoles,"  in  which  may  be  developed  and 
later  shed  into  the  blood-stream  small  parasites.  Within  the  red 
corpuscles  of  man,  when  affected  by  malaria,  are  developed  the  Plus- 
modium  malaria.  Their  passage  into  the  patient's  blood-plasma 
marks  a  paroxysm. 

The  number  of  the  corpuscles  is  usually  spoken  of  in  terms  of 
cubic  millimeters;  thus,  in  man  there  are  about  5,000,000  per  cubic 
millimeter;  in  woman,  about  4,500,000.  These  figures  represent  the 
average  number  per  cubic  millimeter,  but  even  in  health  and  in  the 
same  individual  there  may  be  wide  variations  from  this  standard 
given,  to  say  nothing  of  the  extreme  diminution  experienced  in  cer- 
tain pathological  conditions. 

As  the  corpuscles  are  small  bodies  floating  in  a  liquid  medium, 
the  student  can  easily  understand  why  their  number  should  be  in 
inverse  ratio  to  the  quantity  of  plasma,  when  the  unit,  cubic  milli- 
meter, is  considered.  Copious  sweating  and  the  loss  of  much  water 
by  way  of  the  bowels  and  kidneys  occasion  a  temporary  increase  in 
their  number.  Normally,  there  is  no  difference  as  to  the  number  of 
corpuscles  in  arteries  and  veins,  provided  there  be  no  congestion  in 
the  latter. 

A  most  interesting  variation  is  that  produced  by  habitation  in 
high  altitudes.  A  two  weeks'  sojourn  in  a  high  mountain  has  been 
known  to  show  an  increase  from  5,000,000  to  7,000,000  per  cubic 
millimeter.  This  is  accounted  for  not  because  of  any  real  increase  in 
the  manufacture  of  corpuscles,  but  to  increased  evaporation  with  con- 
sequent loss  of  larger  amounts  of  water.  In  chlorosis  and  pernicious 
anaemia  the  corpuscular  count  falls  considerably.  A  decrease  to  half 
a  million  per  cubic  millimeter  is  the  lowest  limit  compatible  with  life. 

Life-cycle  of  the  Red  Corpuscles. — The  life  of  the  red  corpuscle 
is  unknown.  In  experimental  transfusion  the  red  corpuscles  disap- 
pear at  the  end  of  a  variable  period.  The  destruction  of  blood-cor- 
puscles in  extravasations  does  not  give  us  any  precise  results.  Ob- 
serving the  differences  in  color,  consistency,  and  chemical  reaction,  it 
is  found  that  they  correspond  to  the  different  degrees  of  development. 
This  shows  that  in  the  blood  there  is  a  constant  destruction  and 
renewal  of  the  corpuscles. 

As  to  the  place  of  destruction  of  the  red  corpuscles,  certain  facts 
show  that  the  liver  and  spleen  seem  to  be  places  for  the  accomplish- 
ment of  it. 

Counting  Red  Corpuscles. — Various  methods  have  been  devised 
for  counting  the  number  of  corpuscles,  the  instruments  used  receiv- 


THE  BLOOD. 


131 


ing  the  name  hcemacytometers.  Modifications  are  numerous,  but  un- 
derlying all  of  them  is  one  main  principle,  namely:  the  actual  count- 
ing of  the  corpuscles  within  a  certain  measured  bulk.  To  preserve 
the  shape  and  integrity  of  these  little  bodies  during  the  technique  it 
is  necessary  to  dilute  the  sample  of  blood  with  some  solution  whose 
specific  gravity  exactly  equals  that  of  the  blood-serum.  Some  of  this 
blood-solution  is  then  placed  upon  a  graduated  slide  beneath  a  micro- 


Fig.  17. — Haemacytometer  of  Thoma-Zeiss.     (LAHOUSSE.) 

A,  Capillary  glass  tube.  B,  A  glass  slide  upon  which  is  a  covered  disc 
accurately  ruled  so  as  to  present  1  square  millimeter  divided  into  100  squares 
of  1/20  millimeter  each.  1,  Blood  is  drawn  up  to  this  point.  101  represents 
normal  saline-solution  drawn  up  the  tube,  mixed  with  the  blood  drawn  up  to 
1.  In  101  parts  the  blood  forms  1  part. 

scope  for  counting,  when  the  number  per  cubic  millimeter  is  easily 
computed. 

At  this  point  the  attention  of  the  student  will  be  directed  to  but 
two  instruments :  ( 1 )  the  Thoma-Zeiss  apparatus  and  ( 2 )  the  Daland 
haBmatocrit. 

1.  THOMA-ZEISS  APPARATUS. — The  apparatus  consists  of  two 
separate  and  distinct  parts :  a  capillary  tube  and  a  counting  chamber. 


132  PHYSIOLOGY. 

The  tube  is  for  the  purpose  of  measuring  the  amount  of  blood  whose 
corpuscles  are  to  be  counted.  By  it  also  is  accomplished  the  proper 
dilution  in  the  upper,  bulbed  chamber.  The  capillary  portion  of  the 
tube  is  graduated  to  0.5  and  1.0  marks.  Just  above  the  capillary 
portion  of  the  instrument  is  the  bulbous  portion  containing  a  small 
glass  ball  to  assist  in  the  thorough  mixing  of  blood  and  diluting  nor- 
mal saline  fluid.  Just  above  the  bulb  is  the  101  mark.  For  drawing 
both  blood  and  the  diluting  saline  into  the  apparatus  there  is  at- 
tached a  piece  of  rubber  tubing  with  a  suitable  mouthpiece.  With 
the  blood  up  to  the  1.0  mark  and  enough  diluting  saline  to  bring  the 
whole  quantity  of  liquid  to  101,  the  dilution  is  1  to  100. 

The  second  portion  of  the  instrument,  known  as  the  counting 
chamber,  is  constructed  so  as  to  enable  one  to  count  under  the  micro- 
scope all  the  cells  in  a  known  bulk  of  the  diluted  blood.  In  the  center 
of  a  thick  glass  slide  is  cemented  a  cover-glass  of  accurately  measured 
thickness  with  a  hole  in  the  center  about  1  centimeter  in  diameter. 
In  the  central  area  of  this  cover-glass  is  also  cemented  to  the  glass 
slide  a  glass  disc  about  2  millimeters  smaller  in  diameter  and  exactly 
Y10  millimeter  thinner  than  the  cover-glass.  The  glass  shelf  being 
exactly  1/10  millimeter  thinner  than  the  cover-glass,  it  will  readily 
be  seen  that  if  a  second  loose  cover-glass  be  laid  upon  the  first,  the 
under  surface  of  this  loose  cover-glass  will  be  exactly  Vio  millimeter 
above  the  upper  surface  of  the  glass  disc.  In  this  way  there  is 
secured  a  layer  of  fluid  1/10  millimeter  in  depth.  Furthermore,  1 
square  millimeter  of  the  surface  of  the  disc  is  outlined  and  subdivided 
by  intersecting  lines  into  400  small  squares.  For  convenience  in 
counting,  every  fifth  row  of  squares  is  divided  into  two  by  an  addi- 
tional line.  The  volume  of  diluted  blood  above  each  square  of  the 
micrometer  will  be  1/40oo  cubic  millimeter.  The  average  of  10  or  more 
squares  is  then  ascertained,  which  result  is  multiplied  by  4000  times 
100  to  give  the  number  of  corpuscles  in  a  cubic  millimeter  of  undi- 
luted blood. 

THE  HjEMATOCBlT. — A  rapid  approximate  determination  of  the 
relative  percentage  of  the  corpuscles  may  be  made  by  Daland's  instru- 
ment. The  blood  is  sucked  up  the  graduated  tube  without  dilution  and 
then  centrifuged.  The  corpuscles  rapidly  accumulate  at  the  end  of 
the  tube  in  an  almost  solid  mass  and  their  collective  volume  can  be 
directly  read  off.  The  estimate  can  be  made  with  a  small  quantity  of 
blood,  and  is,  therefore,  capable  of  being  used  for  clinical  purposes. 
Daland  found  that  50  on  the  scale  was  normal;  this,  multiplied  by 
100,000,  gives  the  number  of  corpuscles  in  1  cubic  millimeter. 


THE  BLOOD. 


133 


Experiments  Upon  the  Blood. — Points  of  interest  to  the  physiol- 
ogist particularly  and  the  clinician  incidentally  have  been  disclosed 
as  the  results  of  some  simple  experimental  work  upon  the  blood- 
corpuscles.  Each  red  corpuscle  is  seen  to  be  composed  of  a  fine 
meshwork,  or  stroma,  consisting  of  noncolored,  homogeneous  proto- 
toplasm.  Scattered  throughout  this  framework  is  the  iron-holding 
pigment,  which  gives  color  to  the  corpuscle  and  is  the  substance  with 
which  the  oxygen-gas  enters  into  loose  combination.  Any  reagent 
which  is  able  to  sever  the  union  between  stroma  and  haemoglobin 
causes  the  latter  to  pass  into  solution  in  the  plasma.  The  once-red 
corpuscles  then  appear  as  transparent  bodies.  This  makes  the  blood 
dark  red,  but  transparent,  since  the  coloring  matter  is  in  solution. 
When  the  blood  is  in  this  condition  it  is  said  to  be  "lake-colored." 


Fig.  18. — Red  Blood-corpuscles.     (LANDOIS.) 

a,  &,  Normal  human  red  corpuscles  with  the  central  depression  more  or 
less  in  focus,  c,  d,  e,  Mulberry  forms,  g,  h,  Crenated  corpuscles,  k,  Pale, 
decolored  corpuscles,  i,  Stroma.  f,  Frog's  corpuscles  acted  upon  by  a  strong 
saline  solution. 

Laky  blood  may  also  be  produced  upon  the  injection  of  the  blood- 
serum  of  one  animal  into  the  blood  of  another  kind,  the  serum  having 
the  power  to  destroy  the  red  corpuscles.  The  term  "  globulicidal 
action  "  covers  this  property  of  the  serum. 

The  first  effect  of  pure  water  upon  red  corpuscles  is  to  produce 
a  very  obvious  change  in  shape.  From  being  discoid  in  form,  they 
become  spherical,  or  nearly  so.  After  some  time  the  ha?moglobin 
becomes  dissolved  out,  leaving  the  corpuscles  transparent:  shadow- 
corpuscles.  The  knowledge  thus  gained  led  to  further  research  to 
find  some  solution  which  will  not  affect  the  corpuscles. 

Isotonic  Solutions. — To  prevent  "  laking  "  of  the  blood  normally 
there  must  be  a  certain  degree  of  concentration  of  the  medium  im- 
mediately surrounding  the  corpuscles  so  that  just  sufficient  water 
is  maintained  within  the  corpuscles  as  is  needed.  If  by  the  addition 


134  PHYSIOLOGY. 

I 

of  distilled  water  or  other  reagents  this  degree  of  concentration  is 
changed  so  that  the  balance  is  broken.,  then  too  much  water  enters 
the  corpuscle.  There  immediately  follows  a  change  in  shape,  with 
forcing  out  of  the  pigment.  A  solution  containing  just  enough  of 
salts  so  that  the  corpuscles  are  neither  altered  in  shape  nor  lose  their 
haemoglobin  is  said  to  be  "isotonic."  The  percentage  of  NaCI  neces- 
sary to  generate  such  a  solution  is,  for  frogs'  blood.  0.65  per  cent. ; 
for  blood  of  man,  0.95  per  cent. 

The  action  of  certain  organic  substances  is  of  considerable  im- 
portance. Thus,  bile  and  the  alkaline  salts  of  the  biliary  acids  have 
the  power  to  dissolve  and  destroy  the  red  corpuscles  with  phenomena 
which  resemble  those  produced  by  the  action  of  chloroform.  Urea 
in  solution  also  destroys  them. 

As  to  vitality,  it  is  known  that  the  corpuscles  of  blood  that  have 
escaped  from  the  circulatory  system,  as  well  as  those  from  denbrin- 
ated  blood,  when  reintroduced  into  the  living  blood-stream,  retain 
their  vitality. 

THE  WHITE  CORPUSCLES. 

The  white  corpuscles  are  colorless,  spherical  little  bodies  which 
are  a  little  larger  than  the  red  ones  and  much  less  numerous.  Each 
is  about  1/25oo  inch  in  diameter  and  is  composed  of  granular  proto- 
plasm that  is  highly  refractile  and  without  any  enveloping  membrane. 

In  striking  contrast  to  the  erythrocytes,  the  leucocytes  possess 
not  only  one,  but  usually  three  nuclei ;  even  four  are  not  uncommon. 
Within  the  nuclei  may  be  denned  several  distinct  nudeoli. 

When  examining  a  section  of  blood,  it  is  at  once  a  striking  fea- 
ture how  few  are  the  white  as  compared  with  the  red  corpuscles.  In 
the  average  field  but  three  or  four  are  found,  while  at  the  same  time 
hundreds  of  erythrocytes  are  noticed.  The  average  is  but  1  white  for 
every  500  or  600  red  ones. 

This  proportion  does  not  pretend  to  convey  an  accurate  idea  of 
their  relationship  because  of  the  frequent  fluctuations  of  the  white 
corpuscles  even  in  a  single  day.  They  increase  during  digestion  and 
dimmish  during  abstinence. 

Bleeding,  lactation,  quinine,  local  suppuration,  and  leucocytha> 
mia  increase  the  white  corpuscles;  their  number  is  diminished  by 
large  doses  of  mercury. 

The  proportionate  number  of  leucocytes  that  is  found  in  blood 
drawrn  from  its  containing  vessels  is  no  criterion  of  the  number  found 
within  the  blood-stream.  As  soon  as  blood  is  drawn  from  the  body, 


THE  BLOOD.  135 

for  no  accountable  reason  as  yet  known,  an  immense  number  of  white 
corpuscles  disappears.  It  is  stated  that  there  remain  but  one-tenth 
of  the  number  previously  found  in  circulation. 

Colorless  corpuscles  are  not  essentially  peculiar  to  the  blood- 
stream nor  to  be  found  only  in  it,  for  similar  corpuscles  are  found  in 
lymph,  chyle,  adenoid  tissue,  the  marrow  of  the  long  bones,  and  also 
as  wandering  cells  in  connective  tissue,  drawn  thither  by  inflamma- 
tion and  bacteria. 


Fig.  19. — Leucocytes  of  Man,  showing  Amoeboid  Movement. 
(LANDOIS.) 

Varieties. — According  to  Ehrlich,  they  may  be  separated  into 
three  groups,  the  basis  of  classification  depending  upon  the  staining 
proclivities  of  the  granules  held  within  the  cytoplasm.  To  the  first 
group  he  gave  the  name  eosinophiles,  because  the  granules  of  this 
class  of  corpuscles  stain  best  with  acid  aniline  dyes.  The  basophiles 
comprise  the  second  group  and  include  those  staining  best  with  basic 
dyes.  Last  come  the  neutrophiles ;  their  granules  are  capable  of  being 
colored  only  by  the  presence  of  neutral  dyes.  This  classification  is  a 


136  PHYSIOLOGY. 

very  popular  one  and  one  that  holds  a  very  prominent  position  in 
pathological  circles. 

Another  and  perhaps  easier  classification  is  into  (1)  lymphocytes, 
(2)  mononuclear  leucocytes,  and  (3)  polymorphonuclear  leucocytes. 

1.  LYMPHOCYTES.  —  These   contain  a   single,   round,   vesicular 
nucleus  enveloped  in  a  scanty  supply  of  rather  granular  cytoplasm. 
They  are  derived  from  the  cells  of  the  lymphatic  glands. 

2.  THE  MONONUCLEAR  LEUCOCYTES,  as  the  term  implies,  hold 
but  a  single  nucleus.    They  are  large,  adult-sized  cells,  with  a  vesic- 
ular nucleus  surrounded  by  a  liberal  supply  of  cytoplasm.     They 
possess  certain  amoeboid  movements. 

3.  THE  POLYMORPHONUCLEAR  LEUCOCYTES  are  especially  con- 
spicuous because  of  the  number  and  curious  forms  in  which  their 
nuclei  are  found.     There  may  be  as  many  as  four  or  five  distinct  nuclei 
or  but  one  divided  entirely  or  partially  into  separate  lobes.     As  to 
shapes,  the  horseshoe  and  crescent  are  very  prominent.     These  are 
the  cells  that  are  particularly  active  in  their  amoeboid  movements. 

These  latter  classes  may  represent  but  various  stages  in  the  life- 
history  of  a  single  leucocyte,  the  lymphocyte  representing  the  embryo, 
the  polymorphonuclear  the  adult  cell. 

Amoeboid  Movement. — All  the  leucocytes,  with  the  exception  of 
the  lymphocytes,  have  in  common  a  very  remarkable  attribute  of 
spontaneously  -changing  their  shape  and  thereby  executing  certain 
movements,  which,  from  their  great  similarity  to  those  performed 
by  the  micro-organism  amoeba,  have  been  termed  amoeboid.  When 
the  conditions  of  temperature  and  moisture  are  maintained  at  the 
proper  standard,  the  leucocytes  will  be  seen  slowly  to  alter  their 
shapes  and  to  send  out  from  their  cytoplasm  little  processes  into 
which  the  remainder  of  the  leucocytes  seems  to  flow,  thereby  causing 
a  slight  movement  with  change  of  position.  This  process  repeated 
successively  gives  to  the  cell  its  power  slowly  to  move  from  place  to 
place,  after  having  worked  its  way  through  the  vessel-walls  into  the 
surrounding  connective  tissues.  This  locomotion  is  frequently  termed 
the  "wandering"  of  the  cell.  To  their  sticky  exteriors  there  are  fre- 
quently seen  adhering  fine  pieces  of  broken-down  cells,  bacteria,  and 
other  foreign  particles.  By  reason  of  certain  internal  circulatory 
movements  in  the  protoplasm  of  the  leucocytes,  these  adherent  for- 
eign particles  may  be  drawn  into  the  interior  of  the  cell,  where  some 
are  absorbed,  others  excreted  as  effete  matters. 

Functions  of  the  Leucocytes. — It  is  definitely  known  that  the 
leucocytes  play  an  important  role  in  the  process  of  blood-coagulation. 


THE  BLOOD.  137 

Their  relation  to  this  most  important  process  will  be  discussed  under 
the  head  of  "  Coagulation/'  They  are  believed  to  help  maintain  the 
needed  proportion  of  proteids. 

Their  most  evident  function  is  the  protection  of  the  economy 
from  both  harmless  and  pathogenic  bacteria.  This  they  accomplish 
by  two  methods.  The  first  is  by  generating  a  defensive  proteid  which, 
when  imbibed  by  the  bacteria,  kills  them.  The  second  and  more 
usual  method  is  that  of  drawing  into  their  interiors  the  various 
bacteria,  together  with  the  debris  resulting  from  lesions,  and,  as  it 
were,  eating  them.  From  this  apparent  consumption  of  foreign  par- 
ticles they  have  gained  for  themselves  the  name  of  phagocytes,  and 
the  act  is  known  as  phagocytosis.  The  seat  of  the  presence  of  the 
bacteria  mark  a  miniature  battlefield,  with  the  hosts  of  bacteria 
drawn  up  on  one  side  in  battle  array  against  the  leucocytes,  the  two 
armies  to  become  engaged  in  a  death-struggle.  If  the  leucocytes,  no\v 
termed  phagocytes,  are  victorious,  they  not  only  kill  their  adversaries, 
but  even  remove  every  vestige  of  the  combat,  aided  by  the  fixed  con- 
nective-tissue cells.  Those  leucocytes  which  come  out  of  the  affray 
unharmed,  and  are  no  longer  needed,  find  their  way  back  into  the 
blood-stream. 

If,  however,  the  bacteria  with  their  toxic  secretions  and  excre- 
tions are  too  powerful  for  the  phagocytes,  the  latter  succumb,  to  be- 
come pus-corpuscles.  When  the  pus  has  been  removed  by  drainage 
and  the  action  of  other  leucocytes,,  the  broken-down  tissues  are  re- 
placed by  regenerating  connective  tissues. 

Bacteria  are  not  alone  the  provocation  for  attack  by  the  phago- 
cytes, for  the  presence  of  other  foreign  matters  will  also  call  out  an 
assault.  It  is  well  known  that  surgical  ligatures  of  gut  and  silk  that 
are  allowed  to  remain  within  the  body-cavity  and  tissues  are  grad- 
ually removed,  particle  by  particle,  by  the  phagocytic  action  of  the 
leucocytes. 

The  absorption  of  the  tails  of  tadpoles  and  other  batrachians  is 
due  to  phagocytic  action. 

Diapedesis. — By  reason  of  their  locomotive  tendencies  the  leuco- 
cytes and  red  corpuscles  are  able  to  make  their  way  through  the  walls 
of  the  capillaries ;  this  emigration  has  been  styled  diapedesis.  There 
are  several  stages  before  the  leucocyte  finally  makes  its  exit,  namely: 
slowing  of  the  current  with  the  adherence  of  the  cell  to  the  side  of  the 
blood-vessel,  and  projection  of  processes,  to  be  followed  by  the  gradual 
exit  of  the  entire  leucocyte.  This  process  occurs  to  some  extent  in 
health,  but  is  greatly  exaggerated  by  inflammation,  presence  of  bac- 


138 


PHYSIOLOGY. 


teria,  etc.  Circumscribed  collections  outside  of  the  vessels  often  form 
abscesses,  the  leucocytes  then  receiving  the  name  pus-corpuscles.  The 
leucocytes  in  this  condition  usually  are  dead  and  show  signs  of  fatty 
degeneration.  Frequently  red  corpuscles  follow  in  the  wake  of  the 
white  ones,  passing  through  the  openings  in  the  vessel-walls  made  by 
the  former. 

In  acute  fevers  and  septic  processes,  as  the  temperature  rises 
there  follows  a  decrease  in  the  number  of  erythrocytes,  with  a  corre- 
sponding increase  of  leucocytes. 

Origin  of  Leucocytes. — The  source  of  the  colorless  corpuscles 
seems  to  be  rather  extended.  They  originate  in  the  bone-marrow  and 


© 


.V'V 

I 


Fig.  20. — Blood-plates  and  their  Derivatives.     (LANDOIS.) 

1,  Red  corpuscle  on  the  flat.     2,  On  the  side.     3,  Unchanged  blood-plates. 
4,    Lymph-corpuscle    surrounded    by    blood-plates.      5,    Altered    blood-plates. 

6,  Lymph-corpuscle   with  two   heaps   of   blood-plates   and   threads   of   fibrin. 

7,  Group  of  fused  blood-plates.     8,   Small  group  of  partially  dissolved  blood- 
plates  ,with  fibrils  of  fibrin. 

spleen,  but  the  credit  for  greatest  production  belongs  to  the  lymphoid 
tissues  and  lymphatic  glands.  From  these  latter  sources  the  leuco- 
cytes enter  the  lymph-circulation,  from  thence  to  be  emptied  into  the 
blood-stream.  After  having  once  gained  entrance  to  the  blood-circu- 
lation there  is  rapid  multiplication  to  keep  up  the  proper  supply, 
since  many  succumb  to  the  poisgns  secreted  and  excreted  by  the 
various  bacteria. 

Blood-plates  and  Elementary  Granules. — In  addition  to  the  eryth- 
rocytes and  leucocytes  found  floating  in  the  liquor  sanguinis,  there 
have  been  discovered  other  numerous,  smaller  bodies,  termed  blood- 
plates  and  elementary  granules. 


THE  BLOOD.  139 

The  blood-plates  are  pale  yellow  or  colorless  discs;  round,  oval, 
or  crescentic  in  shape;  and  varying  within  wide  ranges  as  to  size, 
although  ulways  smaller  than  red  corpuscles.  In  blood  that  has  been 
drawn  from  the  vessels  they  diminish  very  rapidly  both  in  numbers 
and  size,  becoming  gradually  dissolved  in  the  plasma  and  are  believed 
to  assist  in  coagulation.  As  to  their  nature,  there  is  some  diversity 
of  opinion,  but  the  consensus  of  thought  seems  to  be  in  favor  of  the 
plates  being  formed  bodies,  and  not  precipitates.  They  have  been 
found  to  contain  the  same  elements  chemically  as  do  the  nuclei  of  the 
leucocytes,  so  that  they  are  probably  fragments  of  the  nuclei  of  dis- 
integrated leucocytes.  In  number,  their  range  is  very  extensive: 
from  15,000  to  200,000  in  a  cubic  millimeter  of  blood. 

The  elementary  granules  are  smaller  than  the  blood-plates  and 
appear  to  be  composed  of  portions  of  the  protoplasm  of  leucocytes. 
They  contain  proteid  and  fatty  matters. 

FORMATION  OF  RED  BLOOD-CORPUSCLES. 

The  red  corpuscles,  as  every  other  portion  of  the  economy,  per- 
form their  allotted  task  and  round  of  existence,  to  finally  die  and 
disappear.  Just  how  long  the  red  corpuscle  lives  is  yet  unknown,  but 
that  it  cannot  be  very  long  lived  is  probable  when  we  consider  that 
its  haemoglobin  is  the  parent-body  of  the  bile-pigments  which  are 
constantly  being  expelled  from  the  body  as  a  portion  of  the  fa?ces. 
Hence  there  must  constantly  be  manufactured  a  new  supply  of  cor- 
puscles to  replace  those  that  die. 

The  origin  of  the  red  corpuscle  as  to  time  may  be  spoken  of  as 
that  which  occurs  during  intra-uterine  life  and  that  occurring  during 
extra-uterine  life. 

During  Intra-uterine  Life. — The  corpuscles  which  first  appear 
in  the  human  embryo  owe  their  existence  to  a  very  simple  origin. 
They  differ  in  some  respects  from  those  that  appear  later  during 
intra-uterine  life,  and  very  materially  from  those  formed  during  life 
outside  of  the  uterus. 

The  wall  of  the  yelk-sac,  situated  entirely  outside  of  the  body 
of  the  embryo,  is  the  seat  of  the  first  vessels  and  blood.  In  the  chick 
the  corpuscles  appear  during  the  first  days  of  incubation  and  before 
the  appearance  of  a  heart.  At  the  end  of  the  first  day,  surround  in.i: 
the  early  embryo  there  appears  a  circular,  vascular  area  made  up  of 
cords  of  cells  in  which  are  developed  the  first  evidences  of  the  ves- 
sels and  corpuscles.  The  corpuscles  appear  in  groups  within  this 
branched  network  of  mesoblastic  cells,  where  they  form  the  "blood- 


140  PHYSIOLOGY. 

islands"  of  Pander.  Presently  the  cords  of  mesoblastic  cells  which 
compose  this  network  begin  to  become  vacuolated  and  hollowed  out 
to  constitute  a  system  of  branching  canals,  at  the  same  'time  that 
their  cells  acquire  the  endothelial  type.  The  small,  nucleated  masses 
of  protoplasm,  known  as  the  "  blood-islands,"  undergo  disintegration, 
whereby  their  nuclei  are  set  free  to  soon  collect  around  themselves  a 
thin  envelope  of  protoplasm.  These  constitute  the  primitive  red 
corpuscles,  and  are  the  only  bodies  contained  within  the  blood  during 
the  first  month.  In  the  meantime  they  have  been  acquiring  a  reddish 
hue,  which  marks  the  advent  of  the  haemoglobin.  As  the  canals  be- 
come extended  and  branched  eventually  to  connect  with  the  heart 
as  its  system  of  vessels,  there  appears  within  them  a  fluid  into  which 
are  emptied  the  red  corpuscles.  Thus  is  completed  the  circulation. 
According  to  Klein,  the  nuclei  of  the  protoplasmic  vessel-walls  multi- 
ply to  form  new  cells.  The  primitive  corpuscles  are  spherical  in 
shape,  nucleated,  and  possess  amoeboid  movements.  They  undergo 
multiplication  by  karyokinesis. 

During  the  foetal  period  the  protoplasm  of  the  connective-tissue 
corpuscles,  derived  from  the  mesoblast,  contains  cells  of  the  size  and 
appearance  of  blood-corpuscles.  The  mother-cells  elongate,  throw 
out  processes  which  become  hollowed  out  and  branched  until  they 
reach  the  regular  circulatory  vessels,  with  which  they  unite  to  empty 
into  them  their  fluid  and  cells.  During  this  period  also  they  seem  to 
be  developed  from  the  liver,  spleen,  and  red  bone-marrow. 

During  Extra-uterine  Life. — For  some  time  after  the  birth  of  the 
mammal,  nonnucleated  corpuscles  are  still  formed  in  the  spleen, 
liver,  and  connective-tissue  cells,  but  by  far  the  most  important  and 
prolific  seat  is  in  the  red  marrow  of  bones.  It  is  in  the  bones  of  the 
skull  and  trunk  and  ends  of  the  long  bones  that  blood-formation  is 
most  extensive ;  the  shafts  of  these  bones  contain  a  yellow,  fatty  sub- 
stance which  is  nonproductive.  Within  the  marrow  is  seen  numbers 
of  nucleated,  red  cells,  which  are  very  similar  to  the  corpuscles  of 
the  embryo,  and,  like  them,  multiply  by  karyokinesis.  From  these 
repeated  divisions  there  result  nonnucleated  red  corpuscles  which  are 
washed  into  the  circulation.  The  blood-forming  cells  have  received 
the  name  of  eryihroblasts,  or  licematoblasts,  and  are  particularly  numer- 
ous after  copious  haemorrhage,  when  the  loss  of  blood  is  being  re- 
placed by  more  active  formation.  At  such  times  some  erythroblasts 
may  appear  in  the  blood-stream,  having  been  forced  out  prematurely, 
so  active  is  the  function  of  the  red  marrow  in  striving  to  repair  the 
damage  done.  These  soon  lose  their  nuclei  while  in  the  blood-stream. 


THE  BLOOD.  m 

If  the  loss  by  haemorrhage  has  been  particularly  severe,  the  yellow 
bone-marrow  and  spleen  assist  in  blood -manufacture,  for  in  the  latter 
and  in  the  splenic  vein  are  found  nucleated,  red  corpuscles  identical 
with  those  of  the  red  marrow  of  bone. 

DESTRUCTION  OF  THE  RED  CORPUSCLES. 

No  exact  time  can  be  given  as  the  life-period  of  an  erythrocyte, 
but  it  is  usually  estimated  to  be  in  the  neighborhood  of  three  or  four 
weeks.  The  student  can  gain  some  comprehension  of  the  number  of 
corpuscles  which  must  constantly  be  undergoing  disintegration  when 
he  recalls  the  fact  that  all  of  the  pigmentary  matters  in  the  body  owe 
their  existence,  directly  or  indirectly,  to  the  hemoglobin  of  these 
little  bodies.  The  quantities  of  urinary  and  biliary  pigments  alone 
that  are  excreted  from  the  economy  are  considerable. 

Physiologists  have  proved  that  there  are  fewer  red  corpuscles  in 
the  hepatic  than  in  the  portal  vein.  The  bile-pigments  are  formed 
by  the  liver-cells;  these  coloring  matters  contain  only  traces  of  iron, 
while  the  hepatic  cells  are  rich  with  it.  They  give  the  characteristic 
test  for  iron  when  treated  with  hydrochloric  acid  and  potassium 
ferrocyanide. 

Traces  only  of  the  iron  are  excreted  as  a  constituent  of  the  bile. 
The  presence  of  iron  in  the  spleen  has  long  made  this  organ  seem  a 
cradle  to  many  physiologists  where  erythrocytes  are  born  and  nour- 
ished. But  the  presence  of  this  same  element  advances  an  argument 
equally  as  strong  in  favor  of  the  spleen  being  the  grave  for  these  same 
little  bodies. 

Pathologically,  masses  of  iron  substances  are  found  within  the 
spleen,  liver,  and  red  bone-marrow  when  abnormal  disintegration 
occurs,  as  in  anaemia. 

CHEMISTRY  OF  THE  CORPUSCLES. 

The  red  corpuscles  consist  of  a  stroma  containing  in  its  meshes 
a  peculiar  proteid  haemoglobin.  Chemically  they  are  made  of  60  per 
cent,  of  water  and  36  per  cent,  of  haemoglobin,  the  remaining  4  per 
cent,  representing  the  stroma,  which  is  made  up  of  lecithin,  choles- 
terin,  and  nucleo-proteid.  The  white  corpuscles  consist  of  solids  and 
water.  The  solids  are  gluco-proteids  and  nucleo-proteids  and  a  small 
amount  of  albumin  and  globulin.  The  protoplasm  may  also  contain 
glycogen  and  fat.  The  nucleus  is  made  up  of  nucleo-proteids,  nuclein, 
and  nucleic  acid.  The  phosphorus  content  of  the  nucleus  is  greater 
than  that  of  the  protoplasm. 


142 


PHYSIOLOGY. 


The  following  table  is  the  result  of  the  analyses  reported  by 
Halliburton : — 

CHEMICAL  COMPOSITION  OF  BLOOD. 
PLASMA. 

Water 90.29% 

C  Serum-   "1 

7.9  % 


Average,  52% 
Maximum,  56.7  % 
Minimum,  45.6% 
Take  100  parts 

T  Proteids 

r    Organic  J 

(8.86%)   | 

J     Serum-    f 
globulin  J 
I  Fibrin     . 

L  Extractives  :     Fats,  etc. 

Solids       , 

^ 

{NaCl 

Soluble 

KC1 

Inorganic  x 

L    (0.85%) 

salts  . 

NaHC08 
Na2HP04 

Insoluble 

salts  . 

f  CaHPO4 
j   CaS04 

0.85% 


100.00% 


COKPUSCLES. 


Average, 
48% 
Maximum, 

Proteids 

Hemoglobin  f  Haematinl 

(27%)             (Fe)      h 
Globulin 

.    27.36% 

54.4% 
Minimum, 
43.3% 

r  Organic 

(30.4%) 

(29.79%)" 

L                          ) 

Crlobul  iri 

.      2.43% 

Take  100-  ; 
parts 

Solids 

Fats    .    .  J 

Lecithin    .  ) 

0.61% 

Cholesterinj 

(31.2*  Y 

KC1 

Inorganic 

(0.8%) 

NaCl 
MaCl2 
CaHP04 

0.80% 

Mg3(P04)2 

Fe  (see  Hsematin). 


100.00% 


The  other  named  constituents  are  common  to  the  two  kinds  of 
corpuscles.  The  mineral  components  are  principally  the  chlorides  of 
potassium  and  sodium  and  the  phosphates  of  calcium  and  magnesium, 


THE  BLOOD. 


143 


the  phosphates  being  in  greater  proportion.  Water  forms  90  per 
cent,  of  the  corpuscular  contents.  It  will  be  remembered  that  the 
sodium  salts  assume  greater  proportions  in  the  plasma.  The  nucleo- 
proteid  obtained  from  the  white  corpuscles  is  the  precursor  of  the 
fibrin-ferment  of  coagulation.  It  is  believed  that  the  proteid  is  con- 
verted into  fibrin-ferment  through  the  activity  of  the  calcium  salts 
of  the  plasma. 

Haemoglobin. — This  is  the  pigment  matter  of  the  red  corpuscles. 
Haemoglobin  is  a  proteid  composed  of  globin,  a  histon,  and  haematin. 
Its  principal  characteristics  are :  (1)  its  ability  to  combine  chemically 
with  oxygen  and  other  gases,  (2)  its  spectroscopic  phenomena,  (3)  its 
crystallization,  and  (4)  the  fact  of  its  containing  iron. 

It  is  by  virtue  of  the  presence  of  this  haemoglobin  that  the  red 
corpuscles  are  capable  of  performing  the  function  of  oxygen-carrying 
• — carrying  it  from  the  external  respiration  in  the  lungs  to  the  internal 
respiration  in  the  cells  of  the  tissues.  The  haemoglobin  molecule 
possesses  the  property  of  linking  to  itself  an  oxygen  molecule,  form- 
ing a  compound  known  as  oxijhcemoglobm.  The  union  of  the  two 
molecules  is  so  unstable  that  the  presence  of  an  easily  oxidized  body, 
or  an  atmosphere  with  a  lower  oxygen  pressure,  separates  the  two, 
the  oxidizable  body  and  the  atmosphere  taking  up  the  oxygen.  Oxy- 
hajmoglobin  minus  oxygen  is  usually  termed  reduced  Jicemo  globin  ;  bet- 
ter, however,  simply  haemoglobin.  Oxyhaemoglobin  is  most  abundant 
in  arterial  blood ;  that  is,  blood  that  has  received  its  oxygen  from  the 
lungs  during  respiration  and  is  then  on  its  way  to  supply  the  needs  of 
the  cells  of  the  tissues.  Oxy haemoglobin  behaves  as  an  acid.  Ordi- 
nary venous  blood  upon  exposure  to  the  air  for  a  considerable  length 
of  time  becomes  bright  red  because  of  the  union  of  the  oxygen  of  the 
air  with  the  haemoglobin  of  the  blood. 

Crystallization  of  Haemoglobin. — The  haemoglobin  is  contained 
within  the  stroma  of  the  corpuscles.  In  form,  the  crystals  of  the 
blood  of  man  and  the  great  majority  of  animals  is  that  of  rhombic 
prisms  or  needles  which  belong  to  the  rhombic  system ;  in  the  squirrel 
there  is  produced  six-sided  plates. 

Haemoglobin  crystals  are  readily  broken  up  by  the  addition  of  an 
acid  or  alkali  into  two  parts:  licematin  &nd.'gloUn.  Hcematin  is  a 
brown  pigment,  representing  the  cleavage  product  of  haemoglobin  in 
the  presence  of  oxygen.  It  contains  all  of  the  iron  of  the  decomposed 
crystals,  and  is  not  crystallizable.  In  addition  to  the  iron,  it  con- 
tains the  four  chief  elements  of  proteid  bodies:  Carbon,  hydrogen, 
oxygen,  and  nitrogen.  Globin  is  the  proteid  element  of  the  haemo- 


144 


PHYSIOLOGY. 


globin.  It  contains  all  of  the  sulphur,  and  constitutes  the  major 
proportion  of  the  haemoglobin  molecule,  which  is  16,000  times  heavier 
than  a  molecule  of  hydrogen. 


Fig.  21. — Blood-crystals  of  Man  and  Different  Animals.     (THAN- 
HOFFEB  and  FREY.) 

1,  Haemoglobin  crystals:  Mo,  squirrel;  Tr,  guinea-pig;  M,  groundmole; 
L,  horse;  Em,  man;  H,  marmot;  Ma,  cat;  T,  cow;  mv,  from  venous 
blood  of  a  cat.  2,  Hsematin  crystals:  E,  man;  Vb,  sparrow;  M,  cat. 
3,  Heematoi'din  crystals  from  an  old  extravasation  of  blood  in  man. 

Haemin. — Ha&min  is  the  decomposition-product  that  results  from 
the  action  of  hydrochloric  acid  upon  haematin.    The  hsemin  crystals 


THE  BLOOD.  145 

are  small  rhombic  plates  and  prisms.  The  finding  of  these  crystals 
of  Teichmann  constitutes  the  best-known  clinical  test  for  the  detec- 
tion of  blood.  The  crystals  are  prepared  by  adding  a  small  crystal 
of  common  salt  to  dry  blood  on  a  glass  slide,  and  then  an  excess  of 
glacial  acetic  acid.  The  preparation  is  then  gently  heated  until 
bubbles  of  gas  are  given  off.  Upon  cooling,  the  characteristic  hsemin 
crystals  are  formed.  By  transmitted  light  the  crystals  appear  as 
mahogany-brown,  but  by  reflected  light  they  are  bluish  black. 

CHEMICAL  PEOPEETIES. — Hsemin  crystals  are  insoluble  in  water, 
alcohol,  ether,  and  chloroform.  Very  strong  sulphuric  acid  is  capable 
of  dissolving  them.  Should  the  solution  be  evaporated  to  dryness 
and  the  residue  properly  treated,  there  will  be  produced  a  brown, 
amorphous  powder.  This  product  is  known  as  licematoporpliyrin. 


•  »V  t    X, 


Fig.  22. — Teichmann's  Hsemin-crystals.     (LAHOUSSE.) 

Hsematoporphyrin  is  iron-free  hsematin.  It  is  frequently  found 
in  pathological  urines,  while  traces  of  it  are  to  be  found  in  normal 
urine. 

It  is  identical  with  bilirubin  in  composition. 

Methaemoglobin.  —  Methaamoglobin  is  prepared  chemically  by 
adding  amyl  nitrite  to  blood.  In  large  doses  amyl  nitrite  is  poisonous 
by  reason  of  arrest  of  tissue-respiration. 

With  carbon-monoxide  gas  (CO)  haemoglobin  jiorms  a  compound 
similar  to  oxy haemoglobin,  but  known  as  carbon-monoxide,  hamoglobin. 
This  union  is  much  more  stable  than  the  preceding,  so  that  when 
carbon-monoxide  gas  is  breathed  in  excess  death  results  from  as- 
phyxia, since  the  tissues  are  prevented  from  receiving  their  proper 
supply  of  oxygen. 

Carbon-monoxide  results  from  the  incomplete  combustion  of 
carbon  in  coal  and  charcoal  stoves.  Its  poisonous  properties  are 
caused  by  its  combining  so  strongly  with  the  haemoglobin  of  the  cor- 


146  PHYSIOLOGY. 

puscles  that  it  prevents  union  with  oxygen,  and  so  produces  asphyxia. 
The  blood  of  both  veins  and  arteries  is  bright,  cherry-red  in  color. 
In  poisoning  from  this  gas,  artificial  respiration  is  sometimes  of  avail, 
with  saline  transfusion. 

For  a  better  understanding  of  the  import  of  the  absorption  bands 
of  the  coloring  matters  in  the  blood,  a  brief  description  will  be  given 
of  the  instrument  whereby  they  are  studied. 

THE  SPECTROSCOPE. 

When  white  light,  or  that  which  reaches  us  from  the  sun,  passes 
from  one  medium  into  another  more  dense,  it  is  decomposed  into  sev- 
eral kinds  of  light,  a  phenomenon  to  which  the  name  dispersion  is 
given.  Thus,  when  a  pencil  of  the  sun's  rays  is  passed  through  a 
prism  of  flint  glass,  it  is  broken  up  into  the  seven  colors  of  the  spec- 
trum. This  band  of  colors  may  be  seen  naturally  in  the  form  of  the 
rainbow.  These  colors  are  violet,  indigo,  blue,  green,  yellow,  orange, 
and  red. 

The  colors  of  the  solar  spectrum  are  not  continuous.  Several 
grades  of  refrangibility  of  rays  are  wanting,  and,  in  consequence, 
throughout  the  whole  extent  of  the  spectrum  there  is  a  great  number 
of  very  narrow,  dark  lines  which  run  at  right  angles  to  the  longi- 
tudinal axis  of  this  band  of  light.  They  are  generally  known  as 
Fraunhofer's  lines,  since  the  most  marked  ones  were  first  mapped 
and  indicated  by  him.  They  are  designated  by  the  letters  A,  B,  and 
(7,  in  the  red ;  D,  in  the  yellow ;  E,  ~b,  and  F,  in  the  green ;  G  and  II, 
in  the  violet. 

If  the  light  produced  from  burning  common  salt  (sodium  chlo- 
ride) be  decomposed  by  means  of  a  prism,  it  will  be  found  to  give  one 
broad  yellow  line.  Artificial  light  will  not  give  Fraunhofer's  lines. 
The  D  line  in  the  solar  spectrum  is  due  to  the  volatilizing  of  the 
metal  sodium  in  the  sun.  Other  elements  account  for  the  remaining 
dark  lines  of  the  spectrum. 

The  spectroscope  is  combined  with  the  microscope  when  making 
a  medico-legal  analysis  of  a  small  amount  of  coloring  matter  resem- 
bling blood.  The  microspectroscope  used  is  generally  the  Sorby- 
Browning  instrument. 

As  will  be  seen  from  the  figure  opposite,  it  is  a  very  compact 
piece  of  apparatus,  very  ingenious  in  construction,  and  consisting  of 
several  parts.  The  prism  is  contained  in  a  small  tube,  which  can  be 
removed  at  pleasure.  Below  the  prism  is  an  achromatic  eyepiece, 
having  an  adjustable  slit  between  the  two  lenses,  the  upper  lens 


THE  BLOOD. 


147 


being  furnished  with  a  screw  motion  to  focus  the  slit.  A  side  slit, 
capable  of  adjustment,  admits,  when  required,  a  second  beam  of  light 
from  any  object  whose  spectrum  it  is  desired  to  compare  with  that  of 
the  object  placed  on  the  stage  of  the  microscope.  This  second  beam 
of  light  strikes  against  a  very  small  prism  suitably  placed  inside  the 
apparatus,  and  is  reflected  up  through  the  compound  prism,  forming 
a  spectrum  in  the  same  field  with  that  obtained  from  the  object  on 
the  stage. 


Fig.  23. — Sorby-Browning  Microspectroscope. 

A  is  a  brass  tube  carrying  the  compound  direct-vision  prism,  and 
has  a  sliding  arrangement  for  roughly  focusing.  5,  a  milled  head, 
with  screw  motion  to  adjust  finally  the  focus  of  the  achromatic  eye- 
lens.  C,  milled  head,  with  screw  motion  to  open  and  shut  slit  ver- 
tically. Another  screw,  It,  at  right  angles  to  C,  regulates  the  slit 
horizontally.  This  screw  has  a  larger  head,  and  when  once  recognized 
cannot  be  mistaken  for  the  other.  D,  D,  an  apparatus  for  holding 


148 


PHYSIOLOGY. 


THE  BLOOD. 


149 


a  small  tube,  that  the  spectrum  given  by  its  contents  may  be  com- 
pared with  that  from  any  other  object  on  the  stage.  E,  a  screw 
opening  and  shutting  a  slit  to  admit  the  quantity  of  light  required 
to  form  the  second  spectrum.  Light  entering  the  aperture  near  E 
strikes  against  the  right-angled  prism  which  I  have  mentioned  as 
being  placed  inside  the  apparatus  and  is  reflected  up  through  the  slit 
belonging  to  the  compound  prism.  If  any  incandescent  object  is 
placed  in  a  suitable  position  with  reference  to  the  aperture  its  spec- 
trum will  be  obtained  and  will  be  seen  on  looking  through  it.  F 
shows  the  position  of  the  field-lens  of  the  eyepiece.  G  is  a  tube  made 
to  fit  the  microscope  to  which  the  instrument  is  applied.  To  use  this 
instrument  insert  G  like  an  eyepiece  in  the  microscope  tube,  taking 
care  that  the  slit  at  the  top  of  the  eyepiece  is  in  the  same  direction 
as  the  slit  below  the  prism.  Screw  on  to  the  microscope  the  object- 
glass  required  and  place  the  object  whose  spectrum  is  to  be  viewed  on 
the  stage.  Illuminate  with  stage  mirror  if  transparent.  Eemove  A 
and  open  the  slit  by  means  of  the  milled  head  H  at  right  angles  to 
D,  D.  When  the  slit  is  sufficiently  open  the  rest  of  the  apparatus 
acts  like  an  ordinary  eyepiece,  and  any  object  can  be  focused  in  the 
usual  way.  Having  focused  the  object,  replace  A  and  gradually  close 
the  slit  till  a  good  spectrum  is  obtained.  The  spectrum  will  be  much 
improved  by  throwing  the  object  a  little  out  of  focus.  Every  part  of 
the  spectrum  differs  a  little  from  adjacent  parts  in  refrangibility,  and 
delicate  bands  or  lines  can  only  be  brought  out  by  accurately  focusing 
their  own  parts  of  the  spectrum.  This  can  be  done  by  the  milled 
head  B.  When  spectra  of  very  small  objects  are  viewed,  powers  of 
V2  inch  to  V20  may  be  employed. 

These  bands  represent  the  light  absorbed  by  the  colored  medium. 
For  the  same  substance  the  bands  are  always  identical  and  similarly 
placed.  Thus,  a  solution  of  oxy haemoglobin  of  a  certain  strength 
gives  two  •'bands,  reduced  hemoglobin  gives  only  one.  The  other  de- 
rivatives, methemoglobin,  hematin,  hemin,  etc.,  though  similar  to 
hemoglobin  when  viewed  with  the  naked  eye,  yet  each  gives  charac- 
teristic absorption  bands  in  various  positions. 

The  amount  of  hemoglobin  as  calculated  by  various  methods  and 
instruments  has  been  found  to  be  in  man,  13.77  per  cent.;  in  woman, 
12.59  per  cent.  Pregnancy  reduces  the  quantity  to  from  9  to  12  per 
cent.  Normally  there  are  two  periods  in  a  person's  life  when  the 
amount  of  hemoglobin  attains  maximum  limits — in  the  blood  of  the 
newborn  and  again  between  the  years  twenty-one  and  forty-five. 
Pathologically  there  follows  a  decrease  during  recovery  from  febrile 


150  PHYSIOLOGY. 

conditions,  as  also  during  phthisis,  cancer,  cardiac  disease,  chlorosis, 
anaemia,  etc. 

It  is  known  that  dry  haemoglobin  contains  0.4  per  cent,  of  iron, 
and  that  all  of  the  iron  of  the  blood  is  held  by  the  haemoglobin  of  the 
red  corpuscles.  The  amount  of  iron  in  the  blood  is  about  45  grains. 

Colorimetric  methods  consist  in  making  comparisons  between  a 
standard  solution  of  a  known  strength  and  the  test  solution  of  blood 
to  be  examined,  water  being  added  to  the  latter  until  the  exact  shade 
of  the  standard  solution  is  obtained. 


Fig.  25. — Von  Fleischl  Haemometer.     (LAHOUSRE.) 

Ar  Mixing  vessel  with  two  compartments:  B,  for  diluted  blood;  C,  for 
pure  water,  reposes  over  the  colored  prism  of  glass,  D.  E,  Scale  to  read  off 
amount  of  hasmoglobin.  M,  A  mirror  to  reflect  light.  H,  Milled  wheel  that 
moves  D.  t 

Von  Fleischl's  Haemometer. — This  instrument  consists  of  A,  a 
cylindrical  cell  for  holding  the  prepared  blood;  Z>,  a  graduated 
wedge-shaped  piece  of  colored  glass  with  which  to  compare  the  solu- 
tion of  blood ;  H,  a  stand  with  a  rack  and  pinion ;  4,  a  capillary  tube 
for  measuring  the  quantity  of  blood  required. 

1.  The  cell  (A)  is  a  cylindrical  metallic  chamber  divided  by  a 
fixed  partition  into  two  equal  compartments,  open  at  the  top,  but 
closed  at  the  bottom  by  a  base  of  glass.  One  of  these  compartments 
is  to  be  filled  with  distilled  water,  the  other  with  the  proper  quantity 
of  blood  dissolved  in  distilled  water. 


THE  BLOOD.  151 

2.  The  colored  glass  wedge  (D)  is  fitted  to  a  metal  frame  so 
that  it  can  be  adjusted  in  the  stand  and  moved  from  side  to  side  by 
the  rack  and  pinion.  When  in  position  the  glass  wedge  moves  directly 
beneath  that  part  of  the  cell  which  contains  the  distilled  water,  thus 
enabling  one  to  compare  the  color  of  the  glass  with  that  of  the  dis- 
solved blood  which  fills  the  adjoining  compartment  of  the  cell.    The 
wedge  is  graduated  at  E  from  1  to  100,  the  figures  representing  the 
percentage  of  hemoglobin  in  the  specimen  of  blood  as  compared  to 
normal  blood  containing  13.7  per  cent,  of  haemoglobin. 

3.  Besides  the  support  for  the  glass  wedge  and  frame,  there  is 
a  white  plaster  mirror  (M)  which  furnishes  the  diffused  light  re- 
quired in  the  test. 

4.  The  capillary  tubes  are  carefully  prepared  to  hold  the  proper 
quantity  of  blood.    The  size  of  these  tubes  varies,  and  on  the  handle 
of  each  is  stamped  a  number  indicating  its  capacity. 

PHYSICAL  PROPERTIES  OF  THE  PLASMA. 

Plasma  is  the  fluid  part  of  the  blood  as  it  occurs  in  a  healthy 
condition  within  the  circulatory  system.  However,  upon  its  removal 
from  the  body  there  is  formed  in  it  a  solid  substance,  called  fibrin, 
from  elements  which  it  previously  held  in  solution.  The  fluid  which 
surrounds  the  clot  is  termed  serum;  it  is  plasma  minus  fibrin.  Plasma 
is  described  as  a  clear,  somewhat  viscid  fluid;  that  of  man,  when 
strata  are  examined,  is  colorless;  when  in  bulk  it  is  slightly  yellow 
because  of  the  presence  of  a  pigment. 

CHEMICAL  PROPERTIES  OF  PLASMA  AND  SERUM. 

In  order  to  examine  plasma,  a  very  great  amount  of  caution  is 
necessary  to  prevent  its  coagulation,  even  after  separating  the  cor- 
puscles. The  most  common  methods  for  obtaining  it  in  a  liquid  state 
are  by  the  use  of  the  "  living  test-tube  " — an  excised  piece  of  jugular 
of  a  horse  filled  with  blood — and  cold  as  an  environment.  It  has  been 
found  that  serum  differs  from  plasma  only  in  respect  to  certain  pro- 
teids,  and,  as  it  is  so  much  easier  to  handle  the  serum,  the  latter  is 
principally  used  for  experimentation. 

Chemically  the  plasma  is  composed  of  inorganic  and  organic  sub- 
stances, with  certain  gases. 

Inorganic  Constituents. — The  plasma's  greatest  factor  is  water. 
It  is  this  which  gives  it  fluidity  and  is  present  to  the  extent  of  90 
per  cent.  There  are  present  many  salts :  sodium  chloride,  carbonate 
of  soda,  chloride  of  potassium,  sulphate  of  potassium,  phosphate  of 


152  PHYSIOLOGY. 

calcium,,  phosphate  of  sodium,  and  phosphate  of  magnesium.  The 
first  two  occur  in  the  greatest  amounts,  the  remaining  ones  only  as 
traces.  It  is  carbonate  of  soda  that  gives  to  plasma  its  ability  to 
absorb  carbonic  acid  and  also  contributes  much  to  its  alkalinity. 

Organic  Constituents. — These  components  are  readily  divisible 
into  proteid  and  nonproteid  groups. 

THE  PROTEIDS  are : — 

1.  One  albumin  (serum-albumin). 

2.  Two  globulins,  termed  serum-globulin  and  fibrinogen. 

3.  A  nucleo-proteid. 

The  classes  of  proteids  present  various  solubilities  in  neutral  sail 
solutions,  by  appreciation  of  which  they  are  able  to  be  separated  from 
one  another. 

The  albumins  upon  half -saturation  with  ammonium  sulphate  re- 
main in  solution,  while  the  globulins  and  nucleo-proteids  are  pre- 
cipitated. The  precipitate  is  removed  by  filtration,  or  the  albumins 
may  themselves  be  precipitated  by  saturation  with  ammonium  sul- 
phate. 

The  globulins  almost  universally  possess  the  characteristic  of 
coagulating  when  heat  of  75°  C.  is  applied  to  them.  In  man  the 
globulins  make  up  about  3  per  cent,  of  the  total  serum. 

Fibrinogen  is  also  a  globulin.  It  is  precipitated  by  half -satura- 
tion with  KaCl,  thus  making  its  differentiation  from  serum-globulin 
a  comparatively  easy  task.  Upon  precipitating  with  NaCl,  if  a  lime 
salt  be  added,  the  precipitate  partakes  of  the  nature  of  a  fibrin-clot 
or  coagulum,  but  is  not  true  fibrin,  since  it  is  a  combination  of  fibrin- 
ogen with  lime. 

Nucleo-proteid  of  Plasma. — About  the  only  characteristic  that 
is  known  in  connection  with  the  nucleo-proteid  is  that  it  is  very 
essential  to  the  formation  of  fibrin  during  coagulation.  It  is  formed 
by  the  dissolution  of  the  leucocytes  and  blood-plates  after  the  blood 
is  shed  from  the  body.  When  hydrocele,  pericardial,  and  ascitic 
fluids  contain  no  leucocytes,  it  has  been  noticed  that  they  lack  power 
of  spontaneous  coagulation.  The  nucleo-proteids  in  the  presence  of 
calcium  salts  form  a  substance  which  is  identical  in  every  respect 
with  the  fibrin-ferment  of  Alexander  Schmidt.  This  new  substance 
possesses  the  power  of  converting  fibrinogen  into  fibrin. 

THE  NONPROTEIDS  OF  THE  PLASMA. — The  nonproteids  comprise 
both  nitrogenous  and  nonnitrogenous  elements. 

The  nonnitrogenous  consist  of  carbohydrates  and  fats,  with  small 
amounts  of  lipochrome  and  sarco-lactic  acid. 


THE  BLOOD. 


153 


The  nitrogenous  elements  comprise  in  their  category  urea,  uric 
acid,  hippuric  acid,  creatin,  and  some  ferments. 

Urea,  which  represents  the  end-product  of  nitrogenous  com- 
bustion of  either  the  tissues  or  the  blood  itself,  and  which  must  be 
included  among  the  normal  elements  of  this  fluid,  is  found  in  the 
blood  in  weak  proportion.  But  it  can  accumulate  in  an  abnormal 
manner  within  the  blood  and  give  rise  to  the  disorder  known  as 
ursemia.  It  is  in  this  way  that  ablation  of  the  kidneys,  acute  nephri- 
tis, and  the  terminal  feverish  period  of  cholera,  in  which  the  urinary 
secretion  is  suppressed,  permit  the  accumulation  of  urea  in  the  blood. 

Uric  acid,  which  is  regarded  as  the  product  of  a  work  of  com- 
bustion less  advanced  than  for  urea,  doubtless  owes  its  existence  to 
an  incomplete  oxidation  of  the  true,  immediate  principles  of  the 
blood.  It  may  occur  in  greater  proportion  than  usual  in  combination 
with  soda,  with  the  urea,  in  the  blood  of  gouty  persons,  and  in  that 
of  albuminuric  persons. 

Gases  of  the  Plasma. — Present  knowledge  affirms  the  presence 
of  oxygen,  nitrogen,  and  carbonic  anhydride.  The  first  two  are 
simply  dissolved  in  the  plasma,  but  the  carbonic  anhydride  occurs  in 
from  43  to  57  volumes  and  then  combines  chemically  with  soda  to 
form  carbonates  and  bicarbonates. 

COAGULATION  OF  THE  BLOOD. 

Normal  blood  contained  within  the  body-vessels  is  a  fluid.  For 
a  very  brief  period  after  it  makes  its  exit  from  a  wounded  vessel  it 
remains  in  a  liquid  state,  but  within  two  or  three  minutes  its  visqdity 
increases  until  there  is  formed  a  solid  of  the  consistency  of  jelly;  to 
this  has  been  given  the  name  blood-dot.  The  process  whereby  the 
clot  is  formed  is  termed  coagulation,  and  is  caused  by  the  presence  of 
a  body  called  fibrin. 

To  observe  best  the  process  of  coagulation,  the  blood  is  drawn 
into  an  open  vessel  as  a  beaker,  care  being  taken  that  the  atmospheric 
and  other  conditions  are  favorable.  The  initial  change  to  occur 
within  the  first  two  or  three  minutes  is  the  formation  of  a  jellylike 
layer  over  the  surface  of  the  blood;  during  the  next  three  or  four 
minutes  this  layer  extends  to  such  a  degree  that  the  entire  blood-mass 
becomes  enveloped.  If  at  this  time  the  contents  of  the  vessel  be 
turned  out,  they  form  a  mold  of  the  exact  shape  of  the  containing 
vessel,  or  the  vessel  may  be  inverted  without  the  escape  of  the  con- 
tents. This  jellylike  mass  is  the  clot.  Within  it  are  imprisoned  the 
serum  and  corpuscles. 


154  PHYSIOLOGY. 

A  straw-colored  fluid,,  the  serum,  is  expressed,  appearing  upon  the 
surface  to  form  finally  a  transparent  layer  of  liquid  around  the  clot. 
The  retraction  is  complete  at  the  end  of  from  twelve  to  twenty  hours, 
at  which  time  all  of  the  serum  has  been  expressed  and  the  corpuscles 
enmeshed  within  the  network  of  fibrin.  The  clot,  so  dense  that  it 
may  readily  be  cut  with  a  knife,  being  heavier  than  the  serum,  is 
found  at  the  bottom  of  the  vessel.  It  is  now  just  about  one-half  of 
its  original  size.  The  serum,  when  examined,  is  found  to  be  prac- 
tically free  from  corpuscles.  The  character  of  the  clot  varies  ac- 
cording to  the  state  of  the  blood.  It  is  large,  soft,  and  tears  easily 
at  times.  At  other  times  it  is  small,  resistant,  and  from  the  energetic 
contraction  of  the  fibrin  the  edges  of  the  upper  surface  of  the  clot 
curve  over  so  as  to  form  a  sort  of  cup. 

The  clotting  of  the  blood  is  due  to  the  development  in  it  of 
fibrin,  whose  fibrils  arrange  themselves  in  the  form  of  a  network. 

In  blood  within  its  vessels  there  are  found  no  such  fibrils  of 
fibrin;  therefore  normally  no  coagulation  occurs  within  the  body. 
These  fibrils  then  must  have  been  formed  by  some  change,  chemical 
or  otherwise,  of  one  or  more  constituents  of  the  blood.  That  the 
corpuscles  themselves  cannot  form  a  clot  excludes  them,  so  that  our 
attention  is  turned  to  the  plasma.  In  it  is  formed  the  fibrin,  for 
pure  plasma  from  which  the  corpuscles  have  been  removed  very 
readily  coagulates.  When  blood  is  vigorously  beaten  with  twigs,  long 
shreds  of  a  nearly  transparent  substance  are  found  adhering  to 
them.  These  are  fibrin-fibers,  free,  or  nearly  so,  from  corpuscles.  Its 
structure  consists  of  very  delicate,  doubly-refractive  fibrils  of  micro- 
scopical size. 

Many  theories  have  been  propounded  to  account  for  the  forma- 
tion of  fibrin  and  the  coagulation  of  the  blood,  but  the  one  most 
widely  received  is  that  of  Hammersten,  a  Swedish  investigator. 

In  the  study  of  plasma  it  was  learned  that  one  of  its  constitu- 
ents was  a  proteid  of  the  globulin  class,  to  which  had  been  given  the 
name  fibrinogen.  It  is  held  in  solution  by  the  plasma  and  believed 
to  be  an  end-product  of  the  disintegration  of  useless  white  corpus- 
cles. Within  the  circulating  fluid  there  is  an  immense  number  of 
these  white  cells;  when  blood  is  withdrawn  from  the  living  vessel 
there  is  a  large  and  very  sudden  destruction  of  them;  according 
to  Alexander  Schmidt,  71.7  per  cent,  are  dissolved.  When  these 
little  bodies  are  disintegrated  in  the  laboratory  they  yield  nucleo- 
proteids ;  so  that  it  is  very  probable  that  practically  the  same  prod- 
ucts result  upon  disintegration  in  the  shed  blood.  To  this  nucleo- 


THE  BLOOD. 


155 


proteid  has  been  given  the  name  prothrombin.  By  the  action  of  the 
calcium  salts  dissolved  in  the  blood-plasma  the  prothrombin  is  con- 
verted into  fibrin-ferment,  or  tlwombin.  When  thrombin  conies  into 
contact  with  the  fibrinogen  molecule  dissolved  in  the  plasma  it  splits 
it  into  two  parts :  one  is  a  globulin,  which  is  very  small  in  proportion 
and  equally  unimportant;  it  remains  in  solution.  The  other  is  the 
insoluble  substance  fibrin,  which  entangles  the  corpuscles  and  is  so 
essential  to  the  formation  of  the  blood-clot. 

The  process  of  fibrin-formation  has  been  neatly  tabulated  by  Dr. 
J.  J.  E.  Macleod/  as  follows : — 

Living  blood 


Plasma 


Albumin      Globulin 


Corpuscles 


White 


Eed 


Ca  salts  +  Prothrombin 


Fibrinogen  -f-  Fibrin  ferment 


Second  globulin 


Fibrin 


Serum 


Clot 


Dead  blood 


To  epitomize,  it  may  be  said  that  coagulation  depends  upon  three 
factors,  according  to  Hammersten's  theory:  (1)  calcium  salts  to  con- 
vert the  nucleo-proteids  in  the  form  of  prothrombin  into  thrombin, 


"  Practical  Physiology." 


156  PHYSIOLOGY. 

or  (2)  fibrin- ferment;  this  latter  breaks  up  the  (3)  fibrinogen  in  solu- 
tion into  an  unimportant  globulin  and  the  all-important  fibrin. 

Fibrin- ferment  is  a  term  used  simply  for  convenience  and  prob- 
ably is  a  misnomer.  It  is  a  proteid  of  the  globulin  group  whose 
substance  does  not  seem  to  be  used  up  in  the  process  nor  to  enter 
into  the  fibrin  formed;  a  small  quantity  of  it  serves  to  break  up  an 
immense  amount  of  fibrin ogen. 

In  the  peculiar  hereditary  disease  of  males  only,  known  as 
haemophilia,  it  sometimes  happens  that  diminished  coagulability  is 
due  to  a  deficiency  of  the  calcium  salts.  Consequently  the  tendency 
to  bleed  may  in  some  cases  be  lessened  by  the  internal  administration 
of  calcium  chloride,  or  the  actual  haemorrhage  may  be  stopped  upon 
its  local  application  or  of  adrenalin. 

A  condition  known  as  buffy  coat  occurs  when  blood  coagulates 
very  slowly.  It  is  most  readily  seen  in  horses'  blood,  being  caused  by 
the  more  rapid  sinking  of  the  red  corpuscles  in  slow  coagulation,  thus 
leaving  the  upper  stratum  to  consist  of  a  layer  of  fibrin  and  white 
corpuscles.  This  whitish  layer  is  elastic,  has  some  resistance,  is  more 
or  less  opaque,  and  has  therefore  been  designated  the  buffy  coat. 

The  shape  of  the  vessel  is  also  a  factor  in  the  production  of  "  buffy 
coat."  If  the  vessel  be  long  and  straight,  the  fall  of  the  corpuscles 
is  facilitated.  The  buffy  coat  then  appears.  No  buffiness,  however, 
is  seen  if  the  vessel  be  large  and  low,  and  if  the  blood  be  received  in 
a  vessel  which  is  shaken  from  time  to  time.  The  blood  of  different 
parts  of  the  vascular  system  shows  differences  as  to  the  time  required 
for  complete  coagulation.  Arterial  blood  coagulates  more  quickly 
than  venous;  blood  of  the  hepatic  veins  coagulates  very  little,  and 
the  same  is  true  of  menstrual  blood — probably  due  in  the  latter  to 
mixture  with  the  alkaline  vaginal  secretions,  for,  when  menstruation 
is  so  abundant  that  this  alkalinity  is  overcome,  then  clotting  may 
ensue. 

Certain  conditions  favor  the  rapidity  of  coagulation.  Clotting 
is  accelerated  by  these  factors:  1.  Calcium  salts.  2.  A  temperature 
a  little  higher  than  that  of  the  body  (102°  to  107°  F.).  3.  Presence 
of  foreign  bodies.  If  a  needle  be  made  to  penetrate  the  wall  of  a 
vessel,  fibrin  is  deposited  upon  it  and  so  produces  coagulation.  It 
seems  to  be  a  sort  of  phenomenon  analogous  to  that  which  occurs 
when  a  thread  is  suspended  in  a  solution  of  sugar,  when  the  crystals 
of  sugar  are  deposited  upon  it.  Injections  of  laky  blood,  biliary  salts, 
fibrin-ferment,  and  rapid  venous  injection  of  a  strong  alkaline  solu- 
tion of  a  nucleo-proteid  also  hasten  coagulation.  4.  Injury  to  the 


THE  BLOOD. 


157 


vessel-walls.  5.  Agitation,  probably  because  there  is  then  a  more 
free  mixture  with  oxygen.  Gelatin  increases  the  coagulating  power 
of  blood,  and  has  been  used  in  haemophilia. 

Coagulation  is  retarded  by:  1.  Oxalates,  which  combine  with 
calcium.  2.  A  very  low  temperature.  3.  The  saturation  of  blood 
with  C02  (thus  in  asphyxia  the  blood  does  not  coagulate).  4.  Blood 
received  into  a  vessel  filled  with  oil  does  not  coagulate.  5.  Coagula- 
tion is  prevented  when  the  blood  is  in  contact  with  normal,  living, 
vascular  walls.  The  addition  of  certain  articles  retards  coagulation ; 
thus,  feeble  doses  of  alkalies,  carbonate  of  sodium  and  potassium, 
sugar,  water,  albumin,  injection  of  peptone,  and  leech  extract.  In 
the  disease  known  as  hemophilia,  as  well  as  in  lightning  strokes,  the 
blood  does  not  coagulate. 

Why  Blood  does  not  Normally  Coagulate  within  the  Blood-vessels. 
— Much  time  and  experiment  have  been  given  to  ascertaining  the 
cause  for  noncoagulation  within  living  walls,  but  withal  the  question 
is  yet  unsettled.  By  some  it  is  thought  that  the  destruction  of  the 
white  corpuscles  is  not  extensive  enough  to  furnish  the  proper  supply 
of  nucleo-proteid,  from  which  fibrin-ferment  is  manufactured.  Ac- 
cording to  Schmidt,  the  blood  within  the  living  vessels  is  constantly 
being  acted  upon  by  two  opposing  influences :  one  with  a  tendency  to 
promote  coagulation,  the  other  to  oppose  it.  In  health  the  former 
never  gains  the  ascendency.  But  perhaps  the  real  secret  depends 
upon  the  intima  being  alive  and  intact. 

Haemorrhage  and  its  Effects. — It  is  common  knowledge  that  a  very 
abundant  loss  of  blood  causes  death.  The  blood  has  for  its  functions 
to  insure  the  physical  conditions  of  the  life  of  the  cells  as  well  as  to 
maintain  an  excitability  of  the  nerve-cells  which  govern  respiration 
and  circulation.  Every  considerable  loss  of  blood  disorders  cell-life 
in  the  organism,  tending  to  cause  death.  Necrosis  very  soon  mani- 
fests itself  when  a  member  has  by  some  procedure  been  deprived  of 
its  normal  supply  of  blood.  When  the  loss  of  blood  has  been  from 
the  whole  system,  and  not  confined  to  any  member,  a  general  death 
precedes  the  local  death  of  the  cells,  because,  the  oxygen  not  going 
to  the  cardiac  and  respiratory  centers,  the  functions  of  the  heart  and 
lungs  are  arrested.  The  principal  symptoms  of  great  loss  of  this  vital 
fluid  are  general  paleness  and  lower  temperature  of  the  cutaneous 
surface,  oppression,  breathlessness,  stoppage  of  the  secretions,  with 
finally  general  convulsions  of  ana?mia. 

The  quantity  of  blood  which  can  be  lost  without  causing  clonth 
varies  according  to  age,  sex,  temperature,  etc.  The  loss  of  some 


158  PHYSIOLOGY. 

cubic  centimeters  in  the  newborn,  of  a  half-pound  in  an  infant  of  one 
year,  or  of  half  the  mass  of  blood  in  an  adult,  is  capable  of  causing 
death.  Women  bear  the  loss  of  blood  much  better  than  men  do 
because  of  the  periodical  haemorrhages  to  which  they  are  subject. 

The  renewal  of  the  blood  appears  to  be  accomplished  rapidly, 
although  the  time  of  withdrawal  plays  an  important  role  in  determin- 
ing whether  there  will  be  attending  fatality.  If  the  loss  has  not  been 
too  severe,  the  fluid  part  of  the  blood  and  its  dissolved  salts  is  replen- 
ished by  withdrawal  from  the  lymph  and  plasma  of  the  tissues.  Later 
the  albumin  is  restored,  but  a  much  longer  period  is  required  for 
replenishment  of  the  corpuscles.  The  amount  of  haemoglobin  is  di- 
minished in  proportion  to  the  amount  of  bleeding. 

SHOCK  very  materially  affects  the  results  of  haemorrhage.  When 
the  sensibilities  are  deadened  temporarily  by  anaesthetics,  less  serious 
results  follow  the  loss  of  a  given  quantity  of  blood  than  do  those  when 
the  same  quantity  escapes  through  accident. 

TRANSFUSION. — This  is  a  process  by  which  blood  is  conveyed 
from  one  animal  to  the  vascular  system  of  another.  It  was  shortly 
after  Harvey's  discovery  of  the  circulation  of  the  blood  that  this 
operation  was  first  practiced  by  Denis,  of  Paris.  He  transfused  the 
blood  of  a  lamb  into  that  of  a  man  with  success.  It  was  believed  that 
a  great  panacea  had  been  discovered  whereby  not  only  blood  lost  by 
haemorrhage  could  be  replaced,  but  a  cure  effected  for  many  diseases 
and  infirmities.  Subsequent  attempts  proved  such  miserable  failures 
that  the  operation  was  abandoned  and  even  proscribed  by  law.  More 
than  a  century  later  it  was  revived,  but  only  after  much  experimenta- 
tion upon  the  lower  animals. 

The  serum  of  certain  animals  possesses  the  property  of  dissolv- 
ing the  red  corpuscles  of  another  species  of  animals.  The  serum 
of  a  dog  destroys  the  red  corpuscles  of  man;  the  haemoglobin  is  dis- 
solved out.  The  serum,  besides  its  action  on  the  red  corpuscles,  is 
also  active  against  the  white  corpuscles  of  the  same  animal,  stopping 
their  amoeboid  movements.  The  globulicidal  action  of  the  serum  is 
related  to  its  poisonous  action  on  microbes.  The  normal  serum  of 
certain  animals  kills  microbes,  as  the  serum  of  the  dog  kills  the 
typhoid  bacilli.  The  power  to  kill  red  corpuscles  and  microbes  is  due 
to  the  presence  in  the  serum  of  a  substance,  an  alexin.  In  transfusion 
this  plays  an  important  part. 

The  knowledge  gained  thereby  was  to  the  effect  that,  for  the 
operation  to  be  at  all  successfully  performed,  blood  of  the  same 
species  of  animal  should  be  used  as  the  one  on  which  it  is  performed. 


THE  BLOOD.  159 

It  was  only  after  the  establishment  of  this  rule  that  it  appeared  pos- 
sible to  determine  the  value  of  transfusion  and  to  make  application 
of  it,  with  some  degree  of  safety,  to  man. 

In  practice  there  are  two  kinds  of  transfusion:  (1)  blood  with 
fibrin ;  (2)  blood  without  fibrin.  In  using  fibrinated  blood  the  stream 
is  passed  directly  from  the  blood-vessel,  either  artery  or  vein,  into 
that  of  the  patient.  Usually  the  peripheral  end  of  a  vein  of  the 
person  furnishing  the  blood  is  united  with  the  central  end  of  a  vein 
of  the  patient.  The  tubing  should  have  been  previously  filled  with 
a  normal  salt  solution  so  as  to  exclude  the  entrance  of  air  into  the 
circulation,  for,  if  sufficient  quantity  of  it  be  introduced,  it  will  be 
carried  to  the  right  side  of  the  heart,  where,  by  virtue  of  the  heart's 
action,  a  froth  will  be  generated,  the  bubbles  from  which,  being 
pumped  into  the  pulmonary  arteries,  arrest  pulmonary  circulation 
and  cause  death.  The  danger  of  coagulation  also  is,  however,  very 
great. 

In  using  defibrinated  blood  the  shed  blood  is  first  whipped  in  an 
open  vessel  with  a  glass  rod  so  as  to  separate  the  fibrin;  it  is  then 
filtered,  heated  to  the  temperature  of  the  body,  and  injected  very 
slowly  into  a  vein  (usually  the  median  basilic)  in  the  direction  of  the 
heart.  Besides  giving  a  tendency  toward  intravascular  coagulation, 
there  is  also  danger  of  introduction  of  bacteria,  whose  entrance  into 
the  injected  blood  occurs  with  the  beating  in  the  process  of  de- 
fibrination. 

It  has  been  learned  that  the  most  serious  symptoms  of  rapid 
haemorrhage  follow  the  sudden  diminution  in  the  amount  of  blood 
in  circulation,  accompanied  with  a  moderate  fall  of  blood-pressure. 
From  these  data  we  conclude  that  the  proper  measures  to  take  are  to 
replenish  the  amount  of  fluid  regardless  of  the  corpuscles  or  the  solu- 
ble nutrient  elements  of  the  plasma.  A  precaution  to  be  taken  is  that 
the  fluid  should  be  of  such  a  density  and  nature  that  no  disturbance 
in  the  vascular  system  be  generated. 

This  knowledge  has  led  to  the  manufacture  of  various  artificial 
solutions  for  infusion,  the  one  most  used  being  a  warm,  sterilized, 
normal  salt  solution  (N"aCl,  0.95  per  cent.)  ;  this  is  injected  either 
subcutaneously  or  into  any  exposed  vein. 

Transfusion  is  called  for  after  copious  hcemorrliage  (acute  anae- 
mia), or  in  such  cases  of  poisoning  when  the  blood-corpuscles  are  no 
longer  capable  of  supplying  the  tissues  with  their  required  supply  of 
oxygen.  This  condition  is  particularly  prominent  in  carbon-monoxide 
(CO)  poisoning. 


1(30  PHYSIOLOGY. 

Plethora. — The  old  physicians  admitted  that  there  were  in  cer- 
tain individuals  of  sanguine  temperament  an  exaggerated  richness 
of  the  mass  of  blood  as  a  consequence  of  too  active  nutrition.  How- 
ever, it  is  impossible  to  verify  in  an  experimental  manner  if  the  mass 
of  blood  be  augmented.  Yet  plethora  is  usually  accompanied  with  a 
swelling  of  the  veins  and  arteries;  an  injection  of  mucous  membrane; 
a  full,  hard  pulse;  congestive  vertigo,  and  dyspnoea  from  pulmonary 
congestion.  Many  physicians  believe  that  there  is  no  such  condition  as 
too  much  blood  in  the  body,  unless  it  be  introduced  experimentally 
by  transfusion.  The  above  symptoms  are  explained  by  reason  of  an 
increased  peripheral  circulation  at  the  expense  of  the  more  central 
one.  Nevertheless,  the  above-named  symptoms  disappear  by  blood- 
letting, which  would  seem  to  admit  the  existence  of  plethora  to  a 
certain  extent. 

An  experimental  plethora  may  be  induced  in  dogs  by  trans- 
fusion; so  that  the  blood  may  be  increased  from  80  to  100  per  cent, 
without  provoking  any  trouble.  The  injected  plasma  is  soon  gotten 
rid  of,  but  the  surplus  corpuscles  remain  for  a  long  time.  There  is 
also  believed  to  be  an  increase  in  the  number  of  red  corpuscles  in 
those  persons  in  whom  for  any  reason  there  should  be  a  suppression 
of  periodically  recurring  haemorrhages,  as  in  menstruation  and  bleed- 
ing from  the  no?o. 

Plethora  of  water,  or  hydrcemia,  follows  the  excessive  ingestion 
of  water.  The  condition  is  but  temporary,  however,  as  an  increased 
diuresis  rapidly  eliminates  the  excess  of  water. 

There  is  a  physiological  excess  of  red  corpuscles  in  the  blood  of 
man  and  animals  who  live  in  high  altitudes. 

MEDICO-LEGAL  TESTS  OF  THE  BLOOD. 

To  determine  that  a  substance  under  examination  and  inspec- 
tion is  blood  several  tests  are  employed : — 

First. — Teichmann's  crystals,  or  hsemin  crystals,  are  a  product 
of  decomposition  of  the  coloring  matter  of  the  blood.  They  may  be 
prepared  by  the  addition  of  glacial  acetic  acid  and  sodium  chloride 
to  the  blood.  A  few  granules  of  dried  blood  are  pulverized  on  a  glass 
slide  with  a  few  granules  of  salt;  having  covered  it  with  a  glass 
circle,  a  drop  of  the  acid  is  allowed  to  flow  under,  when  the  slide  is 
heated.  If  the  examined  substance  be  blood,  the  characteristic  crys- 
tals appear. 

Second. — THE  GUAIACUM  TEST. — On  treating  a  solution  of  the 
coloring  matter  of  the  blood  with  a  fresh  alcoholic  tincture  of  guaia- 


THE  BLOOD. 

cum  and  an  ethereal  solution  of  hydrogen  peroxide,  a  deep-blue 
coloration  is  produced,  due  to  oxidation  of  the  guaiacum  resin. 

Third. — THE  SPECTROSCOPE  TEST,  in  which  characteristic  bands 
appear. 

Fourth. — Careful  measurements  of  the  blood-corpuscles,  their 
diameter,  etc.,  by  means  of  the  microscope  and  photomicrographs. 

Fifth. — UHLENHUTH  TEST.1 — Strong  rabbits  are  injected  sub- 
cutaneously  with  5  cubic  centimeters  of  sterile  human  blood,  the 
injections  being  repeated  every  two  or  five  days,  depending  upon  the 
condition  of  the  test  animal.  The  occurrence  of  a  rise  of  tempera- 
ture above  101°  F.  or  a  decided  loss  in  weight  are  considered  counter- 
indications  to  further  injections  until  after  this  reaction  has  subsided. 
It  is  better  to  give  injections  of  only  5  cubic  centimeters  each  and 
always  with  great  care  as  to  asepsis,  since  abscesses  often  develop  at 
or  near  the  site  of  puncture.  Usually  20  to  30  cubic  centimeters 
make  a  sufficient  quantity  for  the  average-sized  rabbit,  and  with  due 
care  a  specific  anti-serum  can  always  be  produced  in  from  three  to 
four  weeks.  After  a  sufficient  quantity  of  blood  has  been  injected  to 
insure  obtaining  an  anti-serum,  the  rabbit  is  chloroformed,  the  chest- 
cavity  opened,  and  the  blood  drawn  from  the  heart  into  a  sterile 
receptacle  by  means  of  a  sterile  trocar  and  cannula.  The  drawn  blood 
is  placed  in  an  icebox  for  one  hour  until  well  coagulated.  Carbolic 
acid  is  now  added  to  the  serum,  which  has  separated,  sufficiently  to 
make  the  mixture  approximately  0.5  per  cent.  acid.  The  serum  is 
then  drawn  up  into  sterile  pipettes  and  sealed.  It  will  remain  potent 
indefinitely  if  kept  at  a  low  temperature. 

The  test  is  made  as  follows:  A  given  amount  of  the  test-serum 
is  diluted  to  the  desired  extent  with  sterile  water  or  normal  saline 
solution.  To  a  few  cubic  centimeters  of  this  diluted  solution  in  a 
sterile  test-tube  is  added  an  equal  quantity  of  a  similarly  diluted  solu- 
tion of  the  blood  to  be  tested  and  the  tube  left  at  room  temperature  or 
placed  in  an  incubator  for  two  or  three  hours  at  37°  C.  The  reaction, 
if  it  occurs,  will  be  more  rapid  and  marked  if  the  tube  is  exposed  to 
the  higher  temperature.  If  the  dilution  be  sufficient  the  reaction  will 
not  occur  at  room  temperature.  If  the  test-serum  is  used  undiluted 
and  pure  human  blood  is  added  to  it,  the  reaction  is  immediate. 

If  only  the  sample  of  blood  to  be  tested  is  diluted  and  the  test- 
serum  is  used  pure,  the  reaction  is  almost  immediate.  The  reaction 
is  marked  by  a  turbidity  of  the  solution,  becoming  constantly  more 


Dayton,  American  Medicine,,  1903. 

11 


162  PHYSIOLOGY. 

intense.  If  an  old  stain  is  to  be  examined  by  the  serum  test  the 
material  containing  it  is  washed  in  sterile  water  or  in  sterile  normal 
saline,  the  mixture  repeatedly  filtered  and  finally  added  to  some  of  the 
test-serum,  as  in  the  examination  of  fresh  blood  already  described. 

Contamination  with  monkey  blood  can  be  excluded  first  by  a  great 
dilution  of  the  blood  tested,  and  a  dilution  of  the  test-serum  of  1  to 
500,  with  incubation;  second,  by  a  great  dilution  of  the  blood  tested, 
the  test-serum  being  used  pure  and  the  test  made  at  room  temperature. 


CHAPTER   VI. 

THE   CIRCULATION. 

IN  animals  above  the  very  lowest  grades,  as  also  in  plants,  there 
exists  a  particular  liquid  (nutritive  fluid,  blood,  sap),  which  is  agi- 
tated into  a  circular  or  simply  oscillating  movement.  By  reason 
of  this  movement  it  is  permitted  to  reconstitute  itself  unceasingly,  to 
distribute  the  materials  of  nutrition  to  the  different  parts  of  the  or- 
ganism, and  at  the  same  time  carry  away  some  effete  products. 

In  the  lowest  orders  of  animal  life,  as  the  amcebaB  and  infusoria, 
where  no  special  organs  are  manifest  and  no  part  therefore  has  needs 
differing  from  any  other,  there  is  found  no  circulatory  system — no 
heart  or  propelling  body  or  any  blood-vessels.  Its  life  depends  upon 
diffusion  throughout  its  parenchyma  of  substances  brought  from  with- 
out and  of  those  which  must  be  excreted.  It  is  only  as  special  organs 
show  themselves  and  the  liquids  take  determined  directions  toward 
one  or  another  of  them,  that  blood-vessels  are  seen  to  commence ;  these 
at  the  same  time  become  the  receptacles  of  products  absorbed  for  the 
purposes  of  nutrition  and  the  distributors  of  these  same  materials 
to  the  various  tissues  of  the  organism. 

It  is,  therefore,  from  complex  organisms  that  the  idea  of  a  per- 
fect circulation  is  gained,  with  its  admirable  mechanism  for  incessant 
movement  whereby  the  fluid  necessary  for  its  growth,  functions,  and 
individual  life  is  forced  to  every  part.  Viewed  as  a  whole,  the  vascu- 
lar system  of  the  higher  animals  forms  a  system  of  branching  vessels 
or  canals,  closed  in  all  parts,  and  not  showing  at  any  point  in  their 
course  the  least  perceptible  orifice  of  communication  with  the  external 
world.  Consequently,  the  fluids  which  have  to  penetrate  into  the 
closed  channels  of  circulation,  as  well  as  those  which  have  to  emerge 
from  them  for  the  needs  of  secretion  and  nutrition,  only  do  so  by 
passage  through  the  vascular  walls;  that  is,  through  the  finest  filters 
imaginable. 

At  a  variable  point  in  this  tubular  apparatus  there  exists  an 
organ  of  propulsion,  the  heart,  which  is  seconded  in  its  work  by 
auxiliary  means  and  forces  which  aim  to  give  a  determined  and  con- 
stant direction  to  the  movement  of  the  circulatory  fluid. 

(163) 


164  PHYSIOLOGY. 

In  the  study  of  comparative  anatomy  it  is  found  that  certain  lower 
organisms  are  absolutely  without  any  semblance  of  blood-vessels,  yet 
they  absorb  through  the  periphery  of  their  bodies  the  gases  as  well  as 
the  liquids  of  the  fluids  in  which  they  are  plunged,  and,  in  fact,  are 
nourished  and  continue  to  live.  It  is  only  as  animals  with  special 
organs  appear  in  the  scale  of  animal  life  that  there  is  developed  a 
system  of  canals,  more  or  less  complete,  which  are  intended  to  contain 
the  nourishing  fluid.  And  where  there  is  a  circulatory  system  there 
is  present  some  means,  composed — in  the  great  majority  of  cases — of 
muscle,  for  the  impulsion  of  the  circulatory  fluid  to  every  part  of  the 
organism.  Whenever,  in  animal  organisms,  there  is  transformation  of 
energy  into  motion  or  mechanical  work,  it  may  nearly  always  be 
attributed  to  muscle.  So  that  in  the  higher  forms  of  animals  there 
exist  one  or  more  rhythmically  contractile  organs — for  the  most  part, 
muscular  in  nature — to  which  is  attributed  the  task  of  maintaining 
a  definite  circulation. 

Comparative. — Among  insects  and  the  lower  orders  of  Crustacea 
the  heart,  if  such  it  may  be  called,  is  simply  the  contractile  dorsal 
blood-vessel;  among  the  higher  Crustacea,  as  the  lobster,  there  exists 
dorsally  a  well-defined,  muscular  sac.  Among  the  invertebrates  in 
general  the  blood  passes  from  the  arteries  into  irregular  spaces,  known 
as  lacunae,  which  are  situated  in  the  tissues  and  from  which  it  finds 
its  way  back  into  the  veins  to  terminate  in  the  heart  for  the  comple- 
tion of  its  cycle.  That  interesting  creature,  the  amphioxus,  the 
lowest  of  the  vertebrates,  possesses  a  primitive  lacunar  vascular  sys- 
tem. Its  contractile  dorsal  vessel  serves  as  its  systemic  heart;  a  ven- 
tral vessel  serves  as  a  respiratory  heart,  vessels  proceeding  from  it 
to  the  gills.  Fishes  contain  but  a  respiratory  heart,  which  sends 
blood  to  the  gills  for  aeration.  It  consists  of  a  venous  sinus,  an 
auricle,  and  a  ventricle.  From  the  gills  it  finds  its  way  to  the  aorta, 
to  be  distributed  throughout  the  tissues  without  any  further  impul- 
sion. Among  the  amphibians,  as  the  frog,  there  are  found  two  auricles 
with  a  single  ventricle.  Eeptiles  possess  two  auricles  with  two  ven- 
tricles, though  the  latter  are  but  incompletely  separated.  Among 
birds  and  mammals  there  is  a  heart  which  serves  a  double  purpose — 
it  sends  blood  to  the  lungs  for  aeration,  to  the  body  in  general  to 
serve  the  needs  of  its  various  tissues.  The  passage  of  the  blood  to 
the  lungs  is  accomplished  by  the  right  auricle  and  ventricle  and  is 
known  as  the  pulmonary  system.  That  going  to  the  tissues  of  the 
body  is  propelled  by  the  left  auricle  and  ventricle  to  constitute  the 
systemic  system. 


THE  CIRCULATION. 

THE  CIRCULATORY    SYSTEM. 

This  system  has  for  its  distinctive  function  the  propulsion  of  the 
blood  to  every  part  of  the  economy.  It  is  a  closed,  vascular  apparatus 
consisting  of  an  impelling  agency,  or  pump,  with  an  outgoing  and 
incoming  system  of  vessels.  The  central  pumping  organ,  is  the  heart, 
from  which  proceed  the  vessels  that  carry  the  blood  from  the  heart  to 
the  various  organs  and  parts  of  the  body — the  arteries — and  the  ves- 
sels returning  the  impoverished  blood  to  the  right  side  of  the  heart — 
the  veins.  Connecting  the  smallest  arterioles  and  the  fine  radicles  of 
the  beginning  veins  is  a  network  of  microscopical  vessels  large  enough 
in  many  places  to  admit  of  but  a  single  row  of  corpuscles  and  whose 
walls  are  composed  of  a  single  layer  of  endothelial  cells;  these  are 
the  capillaries. 

THE  HEART. 

The  heart  is  a  hollow,  cone-shaped  organ  of  muscle.  It  is  situ- 
ated in  the  cavity  of  the  thorax,  inclosed  by  a  serous  sac:  the  peri- 
cardium. It  lies  between  the  lungs,  rests  on  the  diaphragm,  and  is 
located  more  on  the  left  than  on  the  right  side.  It  is  placed  obliquely ; 
its  broad  end,  or  base,  by  attachments  to  the  blood-vessels,  is  fixed 
to  the  front  of  the  vertebral  column.  The  base  of  the  heart  extends 
from  the  fourth  to  the  eighth  dorsal  vertebra.  The  apex  is  inclined 
downward,  forward,  and  to  the  left,  where  it  terminates  just  behind  the 
interval  between  the  fifth  and  sixth  ribs,  3/4  inch  to  the  inner  side  of 
and  1 1/2  inches  below  the  nipple.  The  heart  is  5  inches  in  length ; 
in  breadth,  3  1/2  inches ;  and  in  thickness,  2  1/2  inches. 

The  heart  is  brown  in  color,  and  on  its  surface  has  a  longitudinal 
and  a  transverse  groove,  which  shows  a  division  of  the  organ  in  four 
parts:  the  two  auricles  and  two  ventricles.  The  heart  increases  in 
all  dimensions  up  to  a  late  period  in  life,  thus  augmenting  its  weight. 
The  auricles  are  cavities  having  thin  walls.  The  base  of  the  heart 
is  formed  by  the  auricles.  A  partition  separates  them  and  they  are 
connected  with  the  great  veins, — the  cavse  and  pulmonary  veins, — by 
which  they  receive  blood  coming  from  every  portion  of  the  system. 
The  aperture  of  communication  between  the  auricles  and  ventricles  is 
the  auriculo-ventricular  opening,  which  permits  the  blood  to  leave  the 
auricle  to  enter  the  ventricle,  but  valves  prevent  it  from  running  back 
into  the  auricle.  The  thick-walled  parts  of  the  heart  are  the  ventricles, 
which  become  thicker  in  the  direction  of  the  apex.  Like  the  auricles, 
they  are  separated  by  a  partition  and  connected  with  the  large  arteries, 
— the  pulmonary  artery  and  aorta, — by  which  they  send  blood  to  the 


16G 


PHYSIOLOGY. 


entire  system.  Both  ventricles  have  valves  called  aortic  and  pul- 
monary, which  prevent  the  reflow  of  the  blood  from  the  arteries  into 
the  ventricles. 

The  right  auricle  consists  of  an  oblong  part,  the  sinus.     The 
walls  of  the 'right  auricle  are  thin  and  translucent,  but  are  thickened 


Fig.  26. — Heart  of  the  Cow,  with  Left  Auricle  and  Ventricle  Laid 
Open.     (MULLER.) 

a,  Root  of  the  aorta,  b,  Spaces  in  the  wall  of  the  auricle,  c,  c,  Orifices 
of  the  pulmonary  veins.  I,  I,  Pulmonary  veins,  p,  p,  Papillary  muscles. 
g,  q,  Columnse  carnese.  A,  Orifice  of  the  aorta.  K,  Left  ventricle.  S,  Septum. 
V,  Left  auricle.  W,  Lateral  wall  of  left  ventricle.  1,  1,  2,  Leaflets  of  mitral 
valve. 

by  means  of  isolated  columns  of  muscle  called  the  pectinate  muscles. 
These  pectinate  muscles  make  the  interior  of  the  heart  present  an 
uneven,  ridgelike  appearance.  On  the  partition  between  the  auricles 
there  is  a  shallow,  oval  fossa,  with  a  border,  and  is  the  position  of  the 
foramen  ovale,  by  which  the  two  auricles  communicated  during  intra- 


THE  CIRCULATION. 


167 


uterine  life.  The  openings  of  small  veins,  the  foramina  Thebesii,  can 
be  seen  at  various  parts  of  the  inner  surface  of  the  right  auricle. 

The  auriculo-ventricular  orifice  of  the  right  side  of  the  heart  is 
a  large  oval  aperture.  It  is  about  an  inch  in  diameter.  It  is  guarded 
by  the  tricuspid  valve,  or  right  auriculo-ventricular  valve. 

The  left  auricle  has  thick  walls,  and  the  walls  are  not  so  trans- 
lucent as  those  of  the  right  auricle.  It  has  a  smooth  interior  surface, 
except  with  the  auricular  appendage,  where  pectinate  muscles  are 


Fig.  27. — Diagram  of  Mammalian  Heart.     (BECLARD.) 

a,  Left  ventricle.  &,  Right  ventricle,  c,  Left  auricle,  d,  Right  auricle. 
f,  Aorta,  g,  g,  Pulmonary  arteries,  h,  Inferior  vena  cava.  i,  Superior  vena 
cava.  k,  Orifice  of  superior  vena  cava.  I,  Orifice  of  inferior  vena  cava. 
m,  Orifice  of  the  coronary  vein,  o,  Left  pulmonary  vein,  p,  Right  pulmonary 
vein,  r,  Orifice  of  the  right  pulmonary  vein,  s,  Orifice  of  the  left  pulmonary 
vein. 

present.  It  has  four  openings,  which  are  the  pulmonary  veins,  two 
in  the  right  and  two  in  the  left  side  of  the  auricle.  At  the  lower 
anterior  part  of  the  cavity  is  the  left  auriculo-ventricular  orifice.  The 
right  ventricle  is  in  the  shape  of  a  pyramid  with  the  base  upward  and 
backward.  It  extends  from  the  right  auricle  to  near  the  apex  of  the 
heart,  and  occupies  more  of  the  front  surface  of  the  heart  than  the  left 
ventricle.  The  walls  of  the  right  ventricle  are  only  one-third  the 
thickness  of  those  of  the  left.  The  septum  ventriculorum  bulges  into 
the  right  ventricle.  There  are  numerous  projecting  ridges  in  the 


168 


PHYSIOLOGY. 


right  ventricle  which  are  muscles  called  the  columnae  carneae.  Some 
of  them  are  named,  from  their  shape,  the  papillary  muscles,  which 
project  from  the  interior  surface  of  the  ventricle  and  end  in  narrow 
tendinous  cords  called  the  chordae  tendineae. 

The  right  auriculo-ventricular  orifice  opens  into  the  ventricle  at 
its  lower  back  part.     From  its  edges  project  a  broad,  membranous 


v.p 


fl 

Fig.  28. — Course  of  Muscular  Fibers  of  Heart.     (LANDOIS.) 

I.  Course  of  the  muscular  fibers  on  the  left  auricle,  with  the  outer  trans- 
verse and  inner  longitudinal  fibers,  the  circular  fibers  on  the  pulmonary  veins 
(v.  p.).    V,  The  left  ventricle.     (John  Reid.) 

II.  Arrangement  of  the  striped  muscular  fibers  on  the  superior  vena  cava. 
a,  Opening  of  the  vena  azygos.     V,  Auricle.     (Elischer). 

fold  divided  into  three  parts  and  hence  called  the  tricuspid,  whose 
free  borders  are  attached  by  the  chordae  tendineae  to  the  papillary 
muscles  and  to  other  points  on  the  interior  surface  of  the  ventricle. 
When  the  valve  is  open  the  three  parts  lie  against  the  interior  surface 
of  the  ventricle.  The  duplicature  of  the  endocardium  with  included 


THE  CIRCULATION. 


1G9 


fibrous  tissue  makes  up  the  tricuspid  valve  and  the  chordae  tendinese. 
The  pulmonary  artery  springs  from  the  base  of  the  right  ventricle. 
Its  opening  is  provided  with  three  semilunar  valves.  These  valves  are 
three  crescentic  doublings  of  the  endocardium  with  fibrous  tissue 
and  arranged  in  a  circle.  Their  convex  border  is  attached  around 
the  edge  of  the  orifice  of  the  artery.  Behind  each  valve  the  artery 
is  dilated  into  a  shallow  pouch,  called  the  sinus  of  Valsalva,  which 
prevents  the  valve,  when  open,  from  adhering  to  the  side  of  the  artery 
and  permits  the  reflow  of  blood  readily  to  press  the  valve  down  to 


Fig.  29. — Course  of  the  Ventricular  Muscular  Fibers.     (LANDOIS.) 

A,  On  the  anterior  surface.  B,  View  of  the  apex  with  the  vortex.  O, 
Course  of  the  fibers  within  the  ventricular  wall.  D,  Fibers  passing  into  a 
papillary  muscle,  P. 

close  the  opening.  At  the  middle  of  the  free  border  of  the  valve  there 
is  a  thickening  of  fibrous  tissue,  making  the  corpora  Arantii.  The 
left  ventricle  is  three  times  the  thickness  of  the  right,  and  its  apex 
forms  the  apex  of  the  heart.  It  is  longer  and  forms  more  of  the 
posterior  surface  of  the  heart  than  the  right  ventricle.  Like  the  right 
ventricle,  it  has  columns  carnese,  papillary  muscles,  and  chorda? 
tendineas. 

The  left  auriculo-ventricular  valve  is  provided  with  a  pair  of 
membranous  folds  forming  the  mitral  valve,  or  bicuspid  valve.     It 


170  PHYSIOLOGY. 

is  larger  in  size  and  thicker  than  the  right  auriculo- ventricular  valve. 
These  mitral  segments  have  the  chordae  tendineae  attached. 

The  left  ventricle  has  an  opening  which  is  the  origin  of  the  great 
blood-vessel,  the  aorta,  which  is  provided  with  semihmar  or  sigmoid 
valves,  of  the  same  character  as  those  of  the  pulmonary  artery. 

Structure  of  the  Heart. 

The  lining  membrane  of  the  heart  is  called  the  endocardium. 
All  the  valves  of  the  heart  are  made  up  by  its  inclosing  fibrous  tissue. 
The  endocardium  is  formed  of  epithelium  and  fibro-elastic  tissue. 
The  rings  to  which  the  valves  are  attached  are  also  made  of  endo- 
cardium and  fibro-elastic  tissue. 

Muscular  Structure   of  the   Heart. 

The  muscular  fibers  of  the  auricles  consist  of  two  kinds.  The 
external  fibers  are  common  to  both  auricles,  while  some  run  into  the 
interauricular  septum.  The  internal  fibers  are  not  common  to  each 
auricle,  but  are  confined  to  each  auricle.  The  fibers  of  the  internal 
layer  are  attached  to  their  respective  auriculo-ventricular  rings.  The 
external  fibers  run  in  a  transverse  direction;  the  internal  fibers  cross 
the  direction  of  the  former.  There  are  other  muscular  fibers,  ar- 
ranged concentrically  around  the  origin  of  the  great  veins  and  auricu- 
lar appendages. 

In  the  ventricles  there  are  several  layers  of  muscles.  The  outer 
layer  runs  from  the  base,  where  they  are  attached  to  the  fibro-car- 
tilaginous  rings  around  the  orifices  toward  the  apex  of  the  heart, 
where  they  run  by  a  sharp  twist  into  the  interior  of  the  left  ventricle 
to  the  papillary  muscles.  This  twisting  of  the  fibers  gives  rise  to  the 
whorl  of  the  fibers  at  the  apex  of  the  heart.  Other  fibers  run  obliquely 
upward  in  the  septum  to  be  attached  to  the  fibro-cartilaginous  ring, 
from  which  they  started.  Still  other  fibers  pass  in  a  horizontal  direc- 
tion into  the  posterior  wall  of  the  left  ventricle  and  take  a  ringlike 
course  in  it. 

The  right  ventricle  in  the  arrangement  of  its  muscular  fibers  may 
be  regarded  as  an  appendage  of  the  left. 

Histology. — The  fibers  of  the  heart  are  striated.  Unlike  the 
voluntary  muscle,  they  branch  and  have  their  ends  united  to  each 
other  so  as  to  form  a  network.  The  open  space  in  the  network  is 
filled  with  connective  tissue  and  lymphatics.  The  muscle-cells  are 
quadrangular  in  shape,  with  a  clear  oval  nucleus.  There  is  no  sar- 
colemma  in  heart-muscle.  The  muscles  of  the  heart  anastomose  and 


THE  CIRCULATION.  171 

divide.  As  to  lymphatics,  it  is  very  liberally  supplied  with  them. 
The  nerves  are  nonmedullated  near  their  ends.  The  muscular  mass 
of  the  heart  is  called  the  myocardium. 

Pericardium. — This  is  a  fibro-serous  sac  inclosing  the  heart,  and 
consists  of  two  leaves,  or  layers.  The  internal  serous,  or  visceral,  layer 
closely  invests  the  heart  and  the  commencement  of  the  great  blood- 
vessels. It  is  an  inextensible  membrane. 

The  external  fibrous,  or  parietal,  layer  is  a  strong,  inelastic  mem- 
brane which  embraces  the  origin  of  the  great  blood-vessels  at  the  base 
of  the  heart. 

These  two  layers  unite  to  make  a  closed  sac.  Between  the  parietal 
and  visceral  layers  is  the  pericardial  liquor,  which  permits  the  two 
layers  to  slide  on  each  other  without  friction.  The  elastic  fibers  in 
the  parietal  layer  permit  of  its  following  very  closely  the  changing 
form  of  the  heart. 

The  Auricles. — In  examining  each  half  of  the  heart  it  is  easy  to 
recognize  that  the  auricle,  on  account  of  the  thinness  and  the  weak- 
ness of  its  muscular  walls,  can  scarcely  be  the  important  part  of  that 
organ.  In  laying  bare  the  heart  of  an  animal  while  artificial  respira- 
tion is  maintained,  it  is  seen  that  the  action  of  the  auricle  is  very  weak 
as  compared  with  that  of  the  ventricle.  A  manometer  introduced  into 
the  auricular  cavity  at  the  moment  when  it  contracts  marks  a  pressure 
that  is  but  one-fifth  or  one-sixth  that  obtained  in  the  corresponding 
ventricular  cavity  and  under  the  same  conditions. 

It  would  seem  that  the  action  of  the  auricle  is  only  accessory  when 
it  is  noted  how  badly  closed  the  cavity  is  on  the  side  toward  the  veins 
and  how  thin  its  walls  are.  With  the  ventricle,  quite  the  reverse  is 
true.  The  walls  are  thick,  the  valves  are  closed  perfectly. 

According  to  Ludwig,  the  principal  role  of  the  auricles  is  to 
render  the  cavity  of  the  ventricles  altogether  independent  of  the 
pressure  of  the  blood  in  the  venous  system ;  also  to  produce  the  closing 
of  the  auriculo-ventricular  valves.  By  its  contraction,  the  auricle  is 
far  from  emptying  itself.  The  fluid  which  it  drives  out  of  its  cavity 
seems  to  be  less  abundant  than  that  which  it  keeps  there. 

The  Ventricles. — The  ventricles  represent  the  parts  that  are 
really  active  in  the  cardiac  circulation.  The  strength  of  the  contrac- 
tions proper  to  the  two  ventricles  reveals  itself  in  the  thickness  of  the 
muscular  walls,  the  fibers  of  which  are  inserted  into  fibrous  rings. 
These  latter  are  the  veritable  skeleton  of  the  heart.  Manometric 
observation  presents  us  with  proof  of  the  force  of  the  ventricular 
contractions. 


172 


PHYSIOLOGY. 


GENERAL  COURSE   OF   THE  CIRCULATION. 

Since  the  main  points  of  the  anatomy  of  the  heart  have  been 
touched  upon,  it  might  be  well  at  this  stage  roughly  to  consider  the 
circuit  of  the  blood  through  it  and  its  vessels.  The  vascular  system 
is  a  closed  apparatus  consisting  of  a  central  pump  with  its  vessels 


t 6 


Fig.  30. — Diagram  of  the  Circulation.     (DuvAL.) 

1,  Left  ventricle.  2,  Left  auricle.  3,  Right  ventricle.  4,  Right  auricle. 
5,  Aorta.  6,  Systemic  capillaries.  7,  Inferior  vena  cava.  8,  Pulmonary 
artery.  9,  Pulmonary  capillaries.  10,  Pulmonary  vein.  11,  Gastric  and  intes- 
tinal vessels.  12,  Intestine.  13,  Portal  vein.  14,  Portal  vein,  forming  second 
capillary  system  in  the  liver.  15,  Liver.  16,  Hepatic  vein.  17,  Pulmonary,  or 
lesser,  circulation.  18  Systemic,  or  greater,  circulation. 

leading  to  every  part  and  organ  of  the  economy.  All  vessels  leading 
away  from  the  heart  are  arteries;  those  leading  toward  it  are  veins. 
The  entire  circuit  of  the  blood  is  divided  into  two  principal 
portions,  which  are  distinctly  separated  from  one  another  both  ana- 
tomically and  functionally.  The  one  conveys  the  blood  to  and  from 


THE  CIRCULATION.  173 

the  lungs  during  the  process  of  aeration;  so  that  to  it  has  been 
affixed  the  term  pulmonary  circulation.  The  other  has  for  its  func- 
tion the  distribution  of  the  blood  to  all  parts  and  organs  of  the 
economy  in  general,  thereby  receiving  the  name  systemic  circulation. 

Beginning  with  the  left  ventricle,  the  blood  is  conveyed  to  the 
aorta,  from  which  branches  are  distributed  to  every  part  of  the  body, 
through  the  capillaries  to  the  veins,  to  be  eventually  returned  as  dark, 
impure  blood  to  the  right  auricle.  This,  the  greater  circuit,  has 
been  termed  the  systemic  circulation.  During  the  course  of  this  cir- 
culation it  has  been  found  that  the  blood  from  the  capillaries  of  some 
of  the  abdominal  viscera  is  gathered  together  into  a  single  vessel,  the 
portal  vein,  which  again  subdivides  to  form  a  capillary  plexus  in  the 
liver.  This  accessory  circulation  is  commonly  designated  as  the  portal 
circulation. 

From  the  right  auricle  the  blood  flows  into  the  right  ventricle, 
from  which  it  is  expelled  through  the  pulmonary  artery  to  the  lungs, 
to  be  returned  to  the  left  auricle  as  bright-red,  pure  blood.  This 
change  in  color  is  due  to  the  presence  of  oxygen  in  the  haemoglobin 
gained  during  the  process  of  aeration.  This  shorter  circuit  is  known 
as  the  lesser,  or  pulmonary,  circulation. 

Difference  of  pressure  between  the  blood  of  the  aorta  and  pul- 
monary artery,  on  the  one  hand,  and  that  in  the  venae  cavse  and  pul- 
monary veins,  on  the  other  hand,  is  responsible  for  the  flow  of  blood. 
Its  direction  is  always  in  the  line  of  least  resistance.  The  greater  the 
difference  of  pressure,  the  greater  is  the  velocity  of  the  blood-stream; 
the  reduction  of  this  difference  to  nil,  as  in  death,  results  in  arrest  of 
movement. 

The  cardiac  revolution  may  be  divided  as  follows:  (1)  the  first 
sound;  (2)  the  first,  or  short,  silence;  (3)  the  second  sound;  and, 
(4)  the  second,  or  long,  silence. 

If  the  cardiac  revolution  be  divided  into  tenths,  then  the  first 
sound  will  be  4/10 ;  the  first  silence,  1/10 ;  the  second  sound,  2/10 ;  and 
the  long  silence,  3/10. 

The  time  of  the  various  acts  of  the  total  cardiac  movement  are, 
according  to  Gibson,  as  follows : — 

Auricular   systole 0.112  second. 

Ventricular   systole 0.368  second. 

Ventricular  diastole 0.578  second. 

The  rhythmical  succession  of  these  acts  constitutes  the  cardiac 
revolution.  By  their  function  the  vital  fluid — the  blood — is  kept  in 
constant  circulation  within  the  body  so  that  every  portion  of  the 


174:  PHYSIOLOGY. 

economy  receives  its  proper  nourishment.  The  processes  of  metab- 
olism are  balanced,  the  various  organs  and  glands  of  the  body  perform 
their  needed  functions,  and  the  whole  animal  lives  and  thrives. 

MOVEMENTS   OF   THE    HEART. 

The  heart  movements  consist  of  alternate  contractions  and  re- 
laxations, which  follow  each  other  with  a  certain  rhythm.  Systole 
is  the  name  for  contraction;  diastole  is  the  term  for  relaxation. 

The  two  auricles  contract  and  relax  synchronously,  and  these 
movements  are  followed  by  a  simultaneous  contraction  and  relaxation 
of  the  ventricles.  There  is  a  systole  and  diastole  of  auricles  and  a 
systole  and  diastole  of  ventricles.  At  last  there  is  a  very  short  period 
in  which  the  heart  is  in  diastole.  The  succession  of  movements  from 
the  commencement  of  one  auricular  systole  to  the  commencement  of 
one  immediately  following  is  known  as  a  cardiac  revolution.  The 
auricular  contraction  is  less  sudden  than  the  ventricular.  The  con- 
traction of  the  auricle  lasts  a  very  short  time,  while  the  time  of  ven- 
tricular contraction  is  considerable,  and  the  relaxation  of  the  ventricle 
is  slow. 

The  time  of  contraction  of  the  auricle  and  its  relation  are  about 
the  same,  but  the  ventricular  diastole  is  nearly  twice  as  long  as  the 
ventricular  systole.  The  auricles  have  a  uniform,  wavelike  move- 
ment; the  ventricles  have  a  spasmodic  action  in  their  movement.  If 
now  the  vena?  cavse  and  pulmonary  veins  are  delivering  blood  into 
the  two  auricles,  then  at  this  time  the  diastole  of  the  auricles  is 
gradually  approaching  completeness.  The  swelling  of  the  auricles  is 
due  in  part  to  the  pressure  in  the  veins  being  greater  than  in  the 
cavity  of  the  auricles  and  in  part  to  the  inspiratory  movement  of 
the  thorax  sucking  the  blood  from  the  veins  external  to  the  thorax 
to  the  interior  of  the  veins  of  the  chest.  During  this  period  the  ven- 
tricles are  filling  with  blood,  for  both  the  tricuspid  and  mitral  valves 
are  open.  As  the  cavity  of  the  auricles  is  smaller  than  that  of  the 
ventricles,  the  auricles  are  filled  sooner  and  consequently  contract 
before  the  ventricles,  the  veins  offering  a  resistance  to  the  backward 
movement  of  the  blood  by  a  narrowing  of  their  opening.  The  systole 
of  the  auricle  forces  the  blood  chiefly  in  the  line  of  least  resistance 
into  the  ventricle,  which  is  not  yet  completely  filled  and  is  under- 
going diastole.  While  the  blood  is  passing  from  the  auricles  into  the 
ventricles  the  auriculo-ventricular  valves  are  floated  gradually  into  a 
horizontal  position.  The  blood  by  the  systole  of  the  auricles  has 
filled  the  ventricles,  already  filled  in  part  during  the  diastole  of  the 


THE  CIRCULATION.  175 

auricle.  Now  the  ventricles  contract,  the  mitral  and  tri cuspid  valves 
are  tightly  pressed  together,  and  regurgitation  of  blood  into  the 
auricles  is  prevented.  As  the  blood  cannot  go  back  into  the  auri- 
cles, it  must  by  the  muscular  force  of  the  ventricles  rush  into  the 
pulmonary  artery  and  aorta,  respectively.  The  onset  of  the  blood 
forces  open  the  semilunar  valves  of  the  pulmonary  artery  and  aorta 
and  exerts  a  pressure  in  these  arteries  partially  filled  with  blood  before 
the  new  rush  of  blood  sets  in.  Their  walls  are  necessarily  consid- 
erably distended.  Then  the  ventricles  dilate  and  at  the  same  time  the 
mitral  and  tricuspid  valves  open,  and  the  semilunar  valves  close  from 
the  recoil  of  blood  against  them.  From  the  time  the  systole  of  the 
ventricles  ends  to  the  full  distension  of  the  auricles,  all  the  chambers 
of  the  heart  are  in  diastole  and  being  filled  with  blood.  This  is  the 
resting  of  the  heart,  and  is  called  the  pause. 

Pathological  Cardiac  Action. — An  increase  in  the  heart' s  action 
is  produced  by  any  resistance  either  in  the  heart  itself  or  in  any  of 
its  blood-vessels.  With  increased  action  the  heart-muscle  undergoes 
hypertrophy,  with  frequent  dilatation  also. 

The  most  common  resistance  met  with  in  the  vessels  is  narrowing 
of  their  lumen  or  want  of  elasticity  in  their  walls.  Within  the  heart 
the  most  usual  defects  are  narrowing  of  the  orifices  or  incompetency 
of  the  valves.  On  account  of  the  latter  condition  blood  is  allowed  to 
escape  in  the  wrong  direction  so  that  the  heart  must  do  extra  work  to 
keep  all  of  it  in  circulation. 

Palpitation  and  syncope  are  two  very  common  conditions  met 
with  and  which  are  due  to  faulty  heart-action,  induced  perhaps  by 
causes  that  are  more  or  less  remote. 

The  Cardiac  Impulse.  —  Synchronous  with  this  act  is  apex-beat, 
by  which  is  understood  that  surface  movement  which  is  seen  or  the 
impulse  that  can  be  felt  within  a  circumscribed  area  and  produced 
by  ventricular  systole.  This  area  is  located  in  the  fifth  left  inter- 
costal space  between  the  mammary  and  midsternal  lines.  The  center 
of  this  area  is  described  as  being  two  inches  below  the  nipple  and  one 
inch  to  its  sternal  side. 

The  cause  of  the  impulse  of  the  heart  is  the  change  in  form  and 
consistency  of  the  ventricles,  when  these  pass  from  the  diastole  to 
the  systole  and  in  the  instantaneous  transformation.  It  is  the  sud- 
den hardening  of  the  ventricle. 

The  impulse  takes  place  at  the  same  time  as  the  systole  of  the 
ventricle,  and  is  caused  by  the  ventricle,  which  is  pressed  very  firmly 
against  the  chest.  At  the  time  of  the  contraction  of  the  ventricle  the 


176  PHYSIOLOGY. 

outline  of  the  heart  changes ;  instead  of  being  an  oblique  cone  having 
an  elliptical  base,  as  at  rest,  it  becomes  a  regular  cone  with  a  regular 
base.  For  giving  more  accurate  accounts  of  the  heart's  movements 
recourse  is  had  to  the  instruments  called  cardiographs. 

Cardiographs. — These  are  instruments  which  give  graphic  rec- 
ords of  the  heart's  movements.  They  register  at  the  same  time  the 
movements  of  the  auricles,  ventricles,  and  the  beating  of  the  heart 
against  the  walls  of  the  chest.  For  obtaining  these  records  of  animals 
the  heart  was  exposed,  levers  attached  to  various  parts  of  it  so  that 
their  distal  ends  could  make  tracings  upon  a  revolving,  blackened 
surface. 

This  apparatus  was  inapplicable  for  use  upon  the  human  heart, 
but  there  are  to-day  for  its  study  numerous  cardiographs,  all  of  them, 
however,  being  only  modifications  of  Marey's  tambours. 


Fig.  31. — Sanderson  Cardiograph. 

Sanderson's  instrument  consists  of  a  hollow  disc,  the  rim  and 
back  of  which  are  of  brass,  while  the  front  is  of  thin  rubber.  On 
its  back  is  a  flat  steel  spring  bent  at  right  angles,  and  its  unattached 
end  is  provided  with  an  ivory  button  which  is  directly  over  the  center 
of  the  rubber  membrane.  The  ivory  button  is  applied  over  the  point 
where  the  apex-beat  is  most  plainly  felt.  During  the  application  of 
the  apparatus  the  ivory  button  is  continually  in  motion  by  the  surface 
pulsations.  Each  movement  of  the  button  sets  the  rubber  membrane 
in  motion,  and,  as  the  drum  is  airtight  and  in  communication  with 
a  second  drum  with  a  recording  lever,  the  diminution  of  air  in  the 
first  causes  an  increase  in  the  content  of  air  in  the  second  and  an 
elevation  of  its  recording  lever  on  a  smoked  drum.  Each  systole 
of  the  ventricle  causes  a  sudden  rise  of  the  lever,  and  the  end  of  the 
systole  is  noted  by  a  marked  gradual  descent  of  it. 

The  cardiogram  is  read  from  right  to  left,  and  normally  shows  a 


THE  CIRCULATION.  177 

small  elevation,  corresponding  to  auricular  systole,  immediately  suc- 
ceeded by  a  very  abrupt  rise  which  marks  ventricular  systole.  This 
is  held  for  0.3  second  presenting  small  vibrations,  which  are  at- 
tributed to  the  closure  of  the  semilunar  valves.  The  downward  stroke, 
very  abrupt,  marks  the  pause,  or  diastole. 

Endocardiac  Pressure. — The  ordinary  mercurial  manometer,  by 
which  the  heart's  work  can  be  estimated,  is  unsuitable  for  determining 
its  ventricular  pressure.  The  objections  are  the  relatively  great 
amount  of  work  required  to  produce  a  given  displacement  of  the  mer- 
cury; that  it  is  not  susceptible  and  sensitive  to  quickly  follow  differ- 
ences of  pressure;  and  when  once  displaced,  the  mercury  possesses 
oscillations  of  its  own  which  confuse  oscillations  of  blood-pressure. 
However,  when  this  instrument  by  the  introduction  of  a  properly 
placed  valve  is  converted  into  a  "maximum  and  minimum  manom- 
eter," the  actual  blood-pressure  may  be  more  readily  determined. 


Fig.  32. — Record  Obtained  with  the  Cardiograph  when  the  Button  is 
Placed  at  the  Apex-beat  of  the  Human  Heart.     (SANDERSON.) 

The  ascent  in  each  curve  is  due  to  the  ventricular  systole. 

The  dog  has  been  very  extensively  used  for  the  application  of  this 
instrument,  from  which  the  appended  figures  are  given: — 

SYSTOLE.  DIASTOLE. 

MAXIMUM  PRESSURE.  MINIMUM  PRESSURE 

Left  ventricle 140  millimeters— 30  to  40  millimeters. 

Right  ventricle 60          "  15 

Right  auricle 20          "  -  7  to    8  " 

By  negative  pressure  is  meant  that  the  mercury  in  the  instrument 
has  been  sucked  toward  the  heart.  The  negative  pressure  as  is  seen 
occurs  only  during  the  diastole  of  the  heart.  Moens  is  of  the  opinion 
that  this  negative  pressure  within  the  ventricle  happens  shortly  before 
the  diastole  has  reached  its  height.  During  negative  pressure  the 
blood  from  the  veins  is  sucked  into  the  heart. 

For  determination  of  the  duration  of  the  cardiac  events,  as  well 
as  the  blood-pressure — that  is,  to  have  tracings  of  the  curves  for  each 
cavity,  to  know  the  time-relations  for  comparison,  as  well  as  the  curves 

12 


178  PHYSIOLOGY. 

of  the  great  arteries  and  veins — requires  an  instrument  of  some  com- 
plexity. Only  within  recent  years  have  these  been  invented,  whereby 
elastic  manometers  counterbalance  the  blood-pressure  instead  of  a 
column  of  liquid.  Many  of  the  instruments  employed  give  their  trac- 
ings from  movements  transmitted  to  them  from  cardiac  sounds  through 
a  tube  to  the  recording  apparatus.  The  sounds  were  usually  appro- 
priately curved  cannulse,  to  one  end  of  which  were  attached  flexible 
rubber  bags,  or  ampullae.  Two  were  introduced  through  the  jugular 
vein  into  the  right  auricle  and  ventricle,  a  third  into  an  intercostal 
space  in  front  of  the  heart.  These  were  put  into  communication  with 
three  tambours  with  their  needles,  by  which  were  recorded  the  endo- 
cardiac  pressure  with  the  duration  of  the  auricular  and  ventricular 
contractions. 

By  these  levers  it  was  shown  without  doubt  that  the  apex-beat  is 
due  to  the  systole  of  the  ventricle,  as  the  two  were  synchronous. 

Clinically,  changes  in  the  cardiac  impulse  are  best  ascertained 
by  using  any  of  the  graphic  instruments  and  then  studying  the  curves 
obtained.  From  such  study  the  observer  is  able  to  get  very  definite 
knowledge  as  to  the  nature  of  the  cardiac  lesion,  its  severity,  etc.  The 
various  stenoses,  insufficiencies,  hypertrophies,  and  dilatations  may  by 
this  means  be  diagnosed  with  considerable  accuracy. 

Persistence  of  the  Heart  Movement. — The  heart  may  continue  to 
beat  for  some  time  after  its  removal  from  the  body.  This  is  par- 
ticularly noticeable  in  cold-blooded  animals  like  the  turtle,  whose 
heart  movements  have  been  known  to  continue  even  for  days. 

When  the  heart  dies  the  ventricles  stop  first,  but  the  right  auricle 
is  the  last  to  be  arrested;  hence  it  is  called  the  ultimum  moriens. 

5OUNDS  OF  THE  HEART. 

When  the  ear  is  placed  over  the  cardiac  region,  or  to  a  stethoscope 
applied  to  the  precordial  area,  two  characteristic  sounds  are  heard. 
The  two  sounds  are  known  as  the  first  and  second,  and  are  emitted 
during  every  cardiac  revolution.  Though  the  sounds  occur  in  quick 
succession,  yet  they  are  each  separated  by  silences. 

The  first  sound  is  the  stronger  of  the  two.  In  nature  it  is  dull. 
It  coincides  with  the  shock  of  the  heart.  The  first  sound  is  followed 
by  the  first,  or  short,  silence. 

The  second  sound  is  shorter  in  duration  and  clearer  in  character. 
It  comes  an  instant  afterward,  at  the  moment  when  the  whole  heart 
is  in  relaxation.  In  pitch,  the  second  sound  is  from  one-fourth  to  one- 
third  higher  than  that  of  the  first  sound. 


THE  CIRCULATION.  179 

Following  the  second  sound  of  the  heart  there  occurs  the  second, 
or  long,  silence.  In  reality  the  pause  occupies  but  a  fraction  of  a 
second,  yet  it  is  said  to  be  "long"  as  compared  with  the  first  silence. 

It  must  be  borne  in  mind  by  the  student  that  there  occur  in  reality 
four  sounds  during  each  cardiac  cycle.  However,  the  first  two  nor- 
mally occur  in  unison,  as  do  the  second  two,  so  that  but  two  sounds  are 
heard  by  the  examiner. 

From  their  difference  in  pitch  the  two  heart-sounds  may  be  ex- 
pressed graphically  upon  the  musical  staff.  To  the  ear  they  simulate 
the  sounds  which  are  produced  in  pronouncing  the  words,  "lubb," 
"dup,"  the  former  corresponding  to  the  first  heart-sound,  the  latter 
to  the  second. 

If  the  two  sounds  be  listened  to  at  some  distance  from  the  heart, 
the  first  may  nearly  always  be  distinguished  from  the  second  by  com- 
paring the  intervals  between  them.  The  time  elapsing  between  the 
first  and  second  sounds  is  generally  much  shorter  than  that  which 
separates  the  second  sound  from  the  first  in  the  succeeding  revolution 
of  the  heart.  But,  in  medical  practice,  too  much  importance  must  not 
be  attached  to  these  intervals,  since  their  respective  duration  is  ex- 
tremely variable.  In  the  absence  of  the  impulse  it  is  better  to  depend 
upon  the  differences  of  pitch. 

Causes  of  the  Sounds. — The  nature  and  causes  of  the  cardiac 
sounds  are  best  studied  in  a  large  mammal  whose  heart-action  is  com- 
paratively slow.  For  this  purpose  the  horse  is  used.  Its  pulse  aver- 
ages but  forty.  The  animal  is  properly  prepared  by  anaesthetizing, 
curarizing,  and  exposing  the  viscus  to  view  by  placing  a  window  in 
the  thorax.  With  stethoscope  and  by  observation  and  palpation,  the 
experimenter  is  ready  to  determine,  among  the  complex  actions  which 
make  up  a  cardiac  cycle,  the  one  which  gives  rise  to  each  of  the 
two  sounds. 

SECOND  SOUND. — The  cause  of  the  second  sound  is  due  to  the 
sudden  closure  of  the  sigmoid  (semilunar)  valves  of  the  aorta  and 
pulmonary  artery  during  relaxation  of  the  ventricle.  The  sudden 
closing  of  the  valves  is  produced  during  the  effort  of  the  arterial 
blood  to  escape  backward  from  the  elastic  reaction  of  the  aorta  and 
pulmonary  artery. 

Proofs  abound  in  support  of  this  theory.  If  the  valvular  move- 
ments be  hindered  in  one  of  the  above-mentioned  arteries  by  placing 
a  clamp  close  to  its  base,  immediately  the  second  sound  is  suppressed 
at  that  point.  If  the  valvular  action  of  both  vessels  be  suppressed,  the 
second  sound  may  be  completely  extinguished. 


180  PHYSIOLOGY. 

Again,  should  the  apex  of  the  heart  be  cut  off  and  the  ventricular 
blood  be  made  to  escape  to  the  outside,  no  second  sound  occurs.  In 
this  experiment  the  sigmoid  valves  have  neither  been  lifted  up  nor 
allowed  to  fall  back  and  stretch  themselves  out  with  a  sound. 

Physically,  one  is  able  to  account  for  the  production  of  the  second 
sound  on  the  principle  that  it  is  produced  by  the  clicking  of  the  sig- 
moid valves.  In  fact,  similar  sounds  are  obtained  b}^  producing  sud- 
den tension  of  a  membrane  under  the  action  of  a  column  of  liquid. 

When  the  initial  stump  of  an  aorta,  whose  valves  are  still  intact, 
is  attached  to  a  tube  and  reflux  of  a  liquid  closes  the  valves,  a  clear, 
snappy  click  is  produced.* 

When  pathological  conditions  occur,  the  sound  is  altered,  being 
accompanied  by  or  even  altogether  superseded  by  a  blowing  sound, 
known  as  a  murmur. 

THE  CAUSE  OF  THE  FIRST  SOUND  is  more  difficult  to  determine 
than  is  that  of  the  second.  The  nature  of  this  sound  is  more  complex, 
several  factors  entering  into  its  evolvement. 

Since  it  is  established  that  the  first  sound  corresponds  in  point 
of  time  with  ventricular  systole,  it  is  reasonable  to  connect  it  with 
one  or  several  phenomena  which  take  place  in  the  heart  at  that 
moment.  They  are:  The  precordial  shock,  contraction  of  the  ven- 
tricles, occlusion  of  the  auriculo-ventricular  valves,  and  opening  of 
the  sigmoid  valves. 

While  the  above  phenomena  are  synchronous  with  the  first  sound, 
yet  the  majority  of  them  are  believed  to  have  no  action  in  producing 
the  first  sound.  Thus,  the  sound  is  audible  in  a  heart  from  before 
which  the  chest-wall  has  been  removed,  so  that  precordial  shock  is  not 
the  source  of  the  sound. 

That  the  opening  of  the  sigmoid  (semilunar)  valves  is  not  of  con- 
sequence has  long  been  refuted  by  experiment. 

In  the  case  of  the  second  sound  we  have  just  learned  that  the 
production  of  it  was  due  to  the  closure  of  the  sigmoid  valves.  In  like 
manner  the  closure  of  the  auriculo-ventricular  valves  is  in  part  the 
cause  of  the  first  sound.  Wintrich,  by  means  of  proper  resonators, 
was  able  to  analyze  the  first  sound  and  so  distinguish  the  clear,  snappy 
valvular  component  of  this  so-called  solid  sound.  The  very  fact  that 
the  sound  is  low  and  booming  in  nature  demonstrates  the  fact  that 
there  must  be  some  other  component  entering  into  its  causation. 

The  tension  and  vibration  of  the  chordae  tendineaB  are  factors  in 
producing  sound,  but  the  nature  of  it  is  similar  in  every  respect  to 
that  produced  by  valvular  vibration. 


THE  CIRCULATION.  181 

Even  though  the  auriculo- ventricular  valves  and  their  chordae 
tendinese  be  destroyed  in  an  excised  heart,  yet  will  there  be  produced 
a  feeble  sound  of  rather  low  pitch.  This  sound  is  believed  to  be  pro- 
duced by  the  contraction  of  the  muscular  fibers  of  ventricular  walls, 
and  has  been  termed  muscle-sound. 

Any  muscle  whatever,  during  its  contraction,  gives  rise  to  a  dull 
sound.  It  is  evident  then  that,  during  contraction  of  the  ventricle, 
this  same  phenomenon  must  occur  and  so  contribute  its  part  to  the 
production  of  the  first  sound. 

From  new  experiments  it  appears  that  the  role  of  the  muscular 
contraction  is  more  important  than  it  has  generally  been  thought  to 
be.  For  verification  of  this  the  following  experiment  seems  to  be 
decisive : — 

The  heart  is  exposed  in  a  dog  that  is  poisoned  with  curare  and  in 
which  artificial  respiration  has  been  maintained  during  two  hours. 
The  left  ventricle  is  cut  open  in  front  and  at  the  back  with  scissors 
along  the  intraventricular  partition.  The  incisions  are  rapidly  length- 
ened from  the  apex  toward  the  base  in  such  a  manner  as  to  turn  com- 
pletely outside  all  the  ventricular  wall.  This  portion  is  no  longer 
held  to  the  rest  of  the  heart  except  by  the  auricle. 

The  suspended  piece  of  ventricular  wall,  under  these  conditions, 
continues  to  contract  with  force  and  rhythm  for  some  seconds.  If 
the  stethoscope  be  applied  to  the  internal  face  of  the  stump,  it  permits 
us  to  hear  at  the  moment  of  each  contraction  a  sound  that  is  exactly 
like  the  one  which  had  been  perceived  in  the  nonmutilated.  There 
is,  however,  a  vast  difference  in  intensity,  the  sound  emitted  from 
the  experimental  heart-muscle  being  very  weak. 

The  contraction  of  the  auricles  is  not  considered  at  all  as  being 
a  factor  in  the  production  of  cardiac  sounds.  Repeated  experiments 
have  proved  the  auricular  contractions  to  be  inaudible. 

Position  of  Valves  and  the  Areas  of  Audibility. — The  pulmonary 
and  tricuspid  of  the  right  lie  nearer  the  surface  than  the  aortic  and 
mitral. 

The  best  point  to  hear  the  pulmonary  valve  is  chiefly  behind  the 
third  left  costal  cartilage.  For  the  aortic  valve  it  is  behind  the  left 
half  of  the  sternum,  on  a  level  with  the  third  space.  For  the  mitral 
valve  it  is  behind  the  left  half  of  the  sternum  on  a  level  with  the 
fourth  and  upper  border  of  the  fifth  cartilage.  For  the  tricuspid, 
behind  the  lower  fourth  of  the  sternum,  to  the  right  of  the  mid.dle 
line  from  the  fourth  right  cartilage  to  a  point  behind  the  junction  of 
the  sixth  right  cartilage  to  the  sternum. 


182  PHYSIOLOGY. 

Variations  in  Heart-sounds. — Increase  in  the  intensity  of  the 
first  sound  of  the  heart  is  indicative  of  a  more  vigorous  contraction 
of  the  ventricles,  with,  of  course,  greater  tension  of  the  auriculo- 
ventricular  valves. 

Increase  of  the  second  sound  denotes  a  higher  tension  in  the  corre- 
sponding large  arteries.  The  condition  is  usually  demonstrative  of 
overfilling  and  congestion  of  the  pulmonary  circuit.  With  equal 
intensity  the  muscular  sound  of  the  left  ventricle  is  appreciably  longer 
than  that  of  the  right. 

Weak  heart-sounds  are  indicative  of  a  feeble  action  of  the  heart 
and  usually  denotes  degenerations  of  the  heart-muscle. 

The  Coronary  Arteries. — The  heart-muscle,  by  reason  of  its  almost 
constant  activity,  must  be  very  generously  supplied  with  blood  to 
insure  its  proper  nutrition.  In  it  are  found  a  system  of  arteries, 
capillaries,  and  veins,  known  as  the  coronary  vessels. 

The  arteries  to  the  heart-muscle  are  two  in  number :  the  right  and 
left  coronary.  They  are  the  first  branches  of  the  aorta,  and  take  their 
origin  just  above  the  level  of  the  free  margins  of  the  semilunar  valves. 
The  diameter  of  the  coronary  arteries  is  that  of  a  crow's  quill.  From 
these  main  vessels  there  proceed  numerous  branches  which  dip  down 
into  the  heart-substance,  dividing  and  subdividing  as  they  go  until  a 
system  of  capillaries  is  formed. 

The  effete  products  are  conveyed  to  the  general  circulatory  system 
by  the  coronary  vein,  which  empties  its  blood  into  the  right  auricle. 

It,  with  its  branches,  is  provided  with  valves,  since  every  auricular 
systole  interrupts  the  venous  flow;  the  ventricular  contractions,  how- 
ever, accelerate  its  flow.  The  coronary  arteries  are  characterized  by 
their  very  thick  connective  tissue  and  elastic  intima,  which  perhaps 
accounts  for  the  frequent  occurrence  of  atheroma  of  these  vessels. 

Ligature  of  the  coronaries  in  the  case  of  dogs  is  followed  by 
very  prompt  results,  because  of  the  sudden  anaemia  and  inability  of  the 
heart  to  rid  itself  of  its  metabolic  decomposition  products.  Within 
two  minutes  the  cardiac  contractions  become  very  irregular,  give  place 
to  twitches,  and  then  cease  all  movements. 

In  those  cases  of  fatty  degeneration  where  growth  of  the  coronary 
vessel-walls  produces  the  condition  known  as  atheroma,  the  symptoms 
of  ligaturing  with  sudden  death  occur  because  of  the  sudden  arrest  of 
the  heart's  action. 

At  the  beginning  of  systole  the  blood  rushes  into  the  coronary 
arteries  in  the  same  fashion  that  it  does  into  other  arteries.  However, 
later,  during  systole,  the  branches  of  the  coronary  arteries  are  so 


THE  CIRCULATION.  183 

squeezed  by  the  strong  ventricular  contractions  that  the  passage  of  the 
blood  is  temporarily  obstructed  or  even  made  to  retrograde.  Before 
the  blood  can  recede  to  any  extent,  systole  has  ended  and  the  blood  then 
flows  along  as  before. 

It  has  also  been  found  that,  during  the  beginning  of  a  ventricular 
systole,  a  cut  into  the  coronary  artery  of  a  living  animal  causes  a 
spurt  of  blood  from  the  central  end  of  the  artery. 

A  shortening  of  the  diastolic  period  lessens  the  nutritive  supply 
to  the  heart.  Diastolic  distension  of  the  left  heart  by  "back  pressure" 
lessens  the  coronary  flow.  These  facts  are  of  much  practical  import 
in  diseases  of  the  heart. 

Frequency  of  the  Heart's  Action. — During  health  the  heart  acts 
so  smoothly  and  with  so  little  concern  on  our  part  that  there  is  required 
considerable  of  self-attention  before  any  differences  are  seen  to  exist. 
Its  action,  as  studied  from  the  throbbings  (pulse)  that  are  exhibited 
by  some  of  the  more  superficial  arteries,  each  of  which  corresponds  to 
ventricular  systole,  is  found  to  lie  in  very  close  sympathy  to  the  other 
great  functions  of  the  economy  and  is  accordingly  influenced  by  them. 
The  average  number  of  adult  beats  is  72  per  minute.  Even  in  health 
great  deviation  on  either  side  of  this  standard  may  exist,  depending 
upon  age,  sex,  size,  food  and  drink,  exercise,  posture,  etc.  That  age 
and  sex  exercise  an  influence  upon  the  frequency  of  the  heart's  move- 
ments must  be  remembered  by  the  clinician  when  making  his  diagnosis. 
From  the  annexed  table  it  will  be  noticed  that  just  before  birth  the 
rate,  as  determined  by  the  stethoscope,  is  very  high,  but  gradually 
diminishes  until  very  old  age,  when  there  is  a  slight  increase.  Sex 
is  very  influential,  the  female  heart  averaging  about  eight  beats  more 
per  minute. 

It  has  been  noticed  that  the  rule  seems  to  be  that  smaller  animals 
possess  a  greater  amount  of  neuro-muscular  activity  than  larger  ones. 
Among  human  beings  this  is  also  applicable,  shorter  people  usually 
having  a  pulse  that  is  a  trifle  more  rapid  than  taller  people.  Idiosyn- 
crasies are  frequently  found  which  are  at  first  very  misleading  to  the 
diagnostician.  Thus,  the  pulse  of  Napoleon  I  often  did  not  exceed 
40  beats  to  the  minute,  yet  he  was  perfectly  well.  After  each  meal 
there  is  an  increase  of  from  5  to  10  beats,  while  following  very 
violent  exercise  the  figures  140  or  150  may  be  reached. 

During  health  there  is  found  a  nearly  constant  relation  existing 
between  the  number  of  heart-beats  and. of  respirations.  This  propor- 
tion is  four  heart-beats  for  every  single  respiration.  Even  when  the 
number  is  very  much  increased  from  violent  exercise  or  any  other 


184 


PHYSIOLOGY. 


cause,  the  proportion  still  remains  constant.     Pathological  conditions 
usually  alter  this  relation.     Landois  gives  the  following  results : — 


AGE. 

PULSATIONS 

PKR    MlXt'TK. 

MALE. 

FEMALE. 

Foetal      

140 

140 

1  year 

128 

128 

105 

105 

2  to  7  years     

97 

98 

8  to  14  years   

84 

92 

14  to  20  years     

76 

82 

40  to  50  years     

70 

78 

Very  old.  age    80  years             .       . 

80 

80 

WORK  OF  THE  HEART. — When  a  force  produces  acceleration,  or 
when  it  maintains  motion  unchanged  in  opposition  to  resistance,  it  is 
said  to  do  work.  To  convey  an  impression  of  the  amount  of  work  done 
by  any  machine,  it  is  usual  to  express  its  efficiency  in  terms  of  work- 
units.  This  is  a  comparatively  easy  task  when  attempted  in  the 
physical  world,  but  becomes  extremely  difficult  when  one  attempts  to 
express  in  terms  of  work-units  the  force  of  the  heart's  action.  The 
work  of  the  heart — central  pump,  that  it  is — is  so  hard  to  reckon  in 
view  of  the  ill-defined  data  that  we  are  able  to  obtain  as  to  the  resist- 
ance which  it  overcomes  and  from  the  fact  that  different  portions  of 
this  human  machine  are  known  to  exert  different  degrees  of  force. 

Anatomical  differences,  then,  in  the  heart  musculature  permit 
the  conclusion  that  the  left  heart,  the  walls  of  which  are  thicker,  has 
more  force  than  the  right  heart.  It  is  reasonable  to  conclude  from 
these  premises  that,  where  the  ventricular  walls  are  three  times 
thicker  in  one  half  of  the  heart  than  they  are  in  the  other,  one  half 
must  have  a  thrice  greater  systolic  force  than  the  other. 

The  work  of  the  heart  is  usually  expressed  in  kilogrammeters.  A 
kilogrammeter  is  equal  to  7.24  foot-pounds.  To  estimate  the  work  of 
the  heart,  according  to  Dr.  Leonard  Hill,  the  mean  pressure  and 
velocity  in  the  aorta  and  the  volume  of  blood  ejected  by  the  ventricle 
must  be  obtained. 

If  W  be  the  work  done  during  systole  of  the  left  ventricle  in 
gram  centimeters;  Q,  the  volume  of  the  output  in  cubic  centimeters; 
M,  the  mass  of  the  output  in  grams;  P,  the  specific  gravity  of  the 
blood  (.*.  M  =  PQ);  V,  the  mean  velocity  in  the  aorta;  H,  the 


THE  CIRCULATION.  185 

mean  aortic  pressure  in  grams  per  centimeter;    g,  the  acceleration 
due  to  gravity  =  981  centimeters  per  second,  then 


...W  =  QH  +  *2p 

The  mean  aortic  pressure  may  be  put  down  as  12  centimeters  of 
mercury  (specific  gravity  of  mercury  =  13.5).  The  volume  of  the 
systolic  output  is  about  110  cubic  centimeters.  Substituting  these 
data  in  the  above  equation  one  obtains : — 

1.05  X  HO  X  322 

W  =  110  +  12  +  13.5  H =  17,880  gram  cen- 

2  X981 

timeters. 

If  in  the  case  of  the  right  ventricle  the  mean  pressure  in  the  pul- 
monary artery  be  taken  to  be  4  centimeters  of  the  mercury,  the  work 
of  that  ventricle  will  be  one-third  of  that  of  the  left  ventricle.  Thus, 
the  total  work  of  each  systole  of  the  heart  will  be  17,880  X  u  = 
23,640  gram  centimeters,  and  the  total  work  of  the  heart  will  be  per 
day  about  24,000  kilogrammeters,  or  1000  kilogrammeters  per  hour, 
or  the  equivalent  of  about  1/50  of  the  whole  amount  of  heat  produced  in 
the  body. 

INNERVATION  OF  THE  HEART. 

If  the  heart  be  removed  from  the  chest  or  all  of  its  nerves  be 
severed,  it  will  still  continue  to  beat  for  a  variable  time,  dependent 
upon  the  class  of  animal  operated  upon.  In  the  case  of  the  frog  and 
other  cold-blooded  animals  the  beating  of  the  heart  will  continue  for 
hours  under  favorable  conditions.  From  this  it  would  seem  that 
there  must  reside  within  the  heart  itself  some  mechanism  whereby  the 
rhythmical  movements  of  the  heart  are  maintained. 

Like  every  other  organ  of  the  body,  the  heart  receives  its  proper 
quota  of  nerve-supply,  through  whose  medium  are  conducted  certain 
impulses  from  without  and  by  whose  influence  its  rhythm  may  be 
altered.  Yet,  in  addition  there  would  seem  to  be  nerve-ganglia  within 
the  heart-substance  which  behave  as  stimuli  to  the  heart  and  so  main- 
tain its  ordinary  rhythmical  movements. 

Cardiac  Ganglia. — This  internal  mechanism  has  been  chiefly 
studied  in  the  frog,  where  there  exist  in  the  heart  three  distinct 


186 


PHYSIOLOGY. 


ganglia:  Bemak's,  Bidder's,  and  von  Bezold's.  From  the  cells  of 
these  ganglia  there  are  discerned  numerous  small  fibers  which  form 
a  plexus  over  the  surface  of  the  auricles  and  upper  portion  of  the 
ventricles. 

Remak's  ganglion  is  seen  at  the  orifice  of  the  superior  vena  cava 
(sinus  venosus).  Bidder's  is  located  at  the  junction  of  the  auricles 
and  ventricles  in  the  auriculo-ventricular  groove.  Von  Bezold's  gan- 
glion has  its  seat  in  the  interauricular  septum. 

The  heart  of  a  mammal  differs  from  that  of  an  amphibian  only 
in  that  there  are  several  groups  of  ganglia  in  the  mammal,,  while  but 
one  exists  in  the  amphibian.  However,  these  several  ganglia  of  the 
mammal  are  believed  to  be  automatically  and  physiologically  equiva- 
lent to  the  homologous  single  ganglion  or  group  of  ganglia  of  the  am- 
phibian. The  same  general  laws  may  be  applied  to  both. 


I 


II 


Fig.  33.— Heart  of  the  Frog.     (I* VON.) 

I.  Anterior  view.  II.  Posterior  view.  A,  A,  Aortae.  Vc,  Superior  vena 
cava.  Or,  Auricle.  V,  Ventricle.  Ba,  Aortic  bulb.  8V,  Sinus  venosus. 
Vci,  Inferior  vena  cava.  Kb,  Hepatic  vein.  Vh,  Pulmonary  vein. 

Cause  of  Cardiac  Rhythm. — The  rhythm  of  the  ventricle  is  a 
property  of  the  cardiac  muscle.  In  the  maintenance  of  this  rhythm 
the  nervous  system  does  not  intervene  except  as  an  ordinary  excitant 
of  muscle.  It  is  known  that,  if  the  apex  of  the  frog's  heart  be  cut 
away,  it  is  then  separated  from  all  ganglia.  The  excised  portion  does 
not  beat  spontaneously,  while  the  rest  of  the  heart,  the  auricle  and  the 
base  of  the  ventricle,  continue  their  rhythmical  action:  Thus  it  seems 
that  the  ventricle  normally  contracts  under  the  persuasion  of  irrita- 
tions which  arise  in  them  from  the  cardiac  ganglionic  cells. 

If  now  the  isolated  and  immovable  portion  of  the  heart  be  placed 
under  a  cardiograph  and  subjected  to  opening  of  the  induction  current, 
there  will  result  a  pulsation  to  each  isolated  induction  shock. 

It  is  a  remarkable  fact  that,  if  this  same  excised  portion  be 
excited  by  frequent  breaks  (at  least  thirty  per  second),  the  muscle 
'beats  rhythmically.  Ordinary  striped  muscle  responds  to  isolated 


THE  CIRCULATION.  187 

and  separate  breaks  of  the  induction  current  by  manifesting  isolated 
contractions.  But  a  condition  of  tetanus  is  produced  under  the  action 
of  a  current  frequently  broken.  Heart-muscle  cannot  be  tetanized. 

Hence  this  observation  would  force  us  to  the  conclusion  that  the 
heart's  rhythm  does  not  depend  upon  the  ganglionic  cells  of  the  heart. 
The  rhythm  is  the  property  of  the  cardiac  muscle  to  react  to  the 
frequent  excitations  which  it  receives. 

In  this  respect  cardiac  muscle  is  completely  differentiated  from 
ordinary  striated  muscle.  It  is  a  mistake  to  seek  to  make  the  rhyth- 
mical property  of  the  cardiac  muscle  a  property  of  ordinary  muscle. 

Theory  of  Cardiac  Rhythm. — The  heart  is  not  equally  excitable 
during  rest  and  during  action;  it  is  less  excitable  during  action  than 
during  waning  action;  that  is,  during  the  beginning  than  during  the 
end  of  systole.  The  comparative  want  of  excitability  is  so  marked 
during  the  commencement  of  systole  that  this  period  has  been  called 
the  refractory  period. 

The  auricles  and  ventricles  do  not  receive  excitations  except  dur- 
ing and  at  the  end  of  diastole  because  of  the  refractory  phase  during 
cardiac  contraction.  It  is  during  diastole  that  the  cavities  of  the 
heart  possess  greatest  excitability.  At  the  end  of  general  diastole 
the  auricles  and  ventricles  are  full  of  blood,  particularly  the  auricles. 

By  reason  of  this  blood-distension  the  auricles  become  excited  and 
contract.  The  blood  is  rushed  into  the  ventricles,  dilating  them  to 
their  maximum.  From  distension  produced  in  them  and  also  from 
ganglionic  impulses  which  were  not  efficacious  except  at  this  moment, 
the  ventricles  are  made  to  contract  in  their  turn. 

With  each  cardiac  cycle  the  same  phenomena  are  manifested,  the 
result  being  a  rhythmical  action  of  the  heart. 

The  warm-blooded  heart  increases  its  pulsations  with  rise  of  tem- 
perature and  decreases  them  correspondingly  with  fall  of  temperature. 
The  temperature  does  not  act  through  the  endocardium,  but  directly 
upon  the  muscle  itself  or  its  ganglia. 

Direct  irritation  of  the  surface  of  the  ventricle  with  tetanizing 
currents  of  electricity  shows  a  marked  change  in  the  rhythm.  Upon 
the  human  heart  the  constant  current  calls  out  an  acceleration  of  the 
heart,  while  an  induction  current  is  without  effect.  Hence,  in  ap- 
parent death  the  proper  current  to  employ  to  stir  up  the  heart  is  the 
constant  current. 

Numerous  experiments  have  been  performed  upon  the  hearts  of 
animals  (the  frog  chiefly)  for  determining  the  causes  and  means  of 
control  of  the  rhythmical  movements  of  the  heart.  The  experiments 


188  PHYSIOLOGY. 

consist,  for  the  most  part,  of  ligaturing  various  portions  of  the  heart, 
and  are  performed  by  tightening  and  then  relaxing  the  ligature  so 
that  the  physiological  connection  is  destroyed,  while  its  anatomical  and 
mechanical  functions  are  still  intact.  The  most  important,  as  well 
as  best  known,  of  the  ligature  experiments  is  the  one  known  as : — 

STANNIUS'S  EXPERIMENT. — If  the  sinus  venosus  of  the  frog's 
heart  be  separated  from  the  auricles  by  the  application  of  a  ligature, 
then  the  auricles  and  ventricles  will  remain  quiet  in  diastole,  while  the 
veins  and  the  remainder  of  the  sinus  continue  to  beat.  If  a  second 
ligature  be  applied  at  the  junction  of  the  auricles  and  ventricle,  the 
usual  sequence  is  for  the  ventricle  to  begin  to  beat  again  while  the 


Fig.  34. — Schema  of  Ligatures  of  Stannius.     (HEDON.) 

A.  Ligature  below  the  auriculo-ventricular  groove  (L);-the  sinus  venosus 
(3)  and  the  auricles  (1)  continue  to  beat,  but  the  apex  of  the  isolated  ventricle 
is  arrested. 

B.  Ligature  of   L   to   sinus   (3),   which   continues  its  rhythmical   beats;   1 
and  2  are  arrested  in  diastole   (seventh  experiment  of  Stannius). 

C.  After  the  ligature  (L)  as  in  B,  a  second  ligature  (L')  is  placed  around 
the  auriculo-ventricular  groove;    the  ventricle,  which  was  originally  arrested, 
after  some  rhythmical   contractions,    is  again   arrested  (tenth  experiment  of 
Stannius). 

auricles  continue  to  remain  in  their  diastolic  rest.  Though  the  two, 
sinus  venosus  and  ventricle,  continue  to  beat,  their  motion  is  not 
rhythmical,  the  ventricular  movements  being  considerably  slower. 
In  every  case  the  quiescent  portion  can  be  made  to  give  single  con- 
tractions by  stimuli,  either  mechanical  or  electrical.  Thus,  when 
the  ventricle  remains  quiet  after  the  first  ligature,  it  may  be  made 
to  give  single  contractions  by  pin-pricks. 

To  explain  the  experiment  of  Stannius  it  has  been  asserted  that 
Remak's  and  Bidder's  ganglia  are  motor  and  von  Bezold's  is  inhibi- 
tory; that  the  motor  influence  of  Remak's  and  Bidder's  is  greater 
than  the  inhibitory  influence  of  von  Bezold's;  hence,  in  the  absence 
of  all  ligatures,  the  heart  beats.  That  the  motor  power  of  Bidder's  is 


THE  CIRCULATION.  189 

less  than  the  inhibitory  power  of  Ludwig's;  consequently,  the  first 
ligature  cutting  off  the  motor  power  of  Kemak's,  the  auricle  and  ven- 
tricle stand  quiescent,  while  after  the  second  ligature,  cutting  off  also 
the  inhibition  of  von  Bezold's  ganglia,  the  ventricle,  actuated  by  Bid- 
der's ganglia  alone  and  unopposed,  again  commences  to  beat. 

According  to  Gaskell  and  Englemann,  the  nerve-ganglia  do  not 
play  any  part  in  the  movements  of  the  frog's  heart.  According  to 
their  ideas  the  sinus  sends  out  impulse-waves  through  the  muscular 
structure  of  the  heart.  When  the  first  Stannius  ligature  is  applied  it 
blocks  the  waves  running  from  the  sinus  to  the  right  auricle.  Here 
the  sinus  continues  beating,  but  the  remainder  of  the  heart  is  quiet. 
If,  now,  you  tie  a  ligature  in  the  auriculo-ventricular  groove  of  this 
quiescent  heart,  then  the  ventricle  beats.  The  ligature  or  compressor 
at  this  point  is  said  to  stimulate  the  ventricle. 

Extracardiac  Nervous  System. 

The  extracardiac  nervous  system  is  composed  of  the  cardiac 
branches  of  the  vagus,  together  with  the  cardiac  branches  of  the 
sympathetic. 

The  Vagus. — The  superficial  origin  of  this  nerve  is  from  the 
groove  between  the  inferior  olive  and  the  restiform  body.  It  leaves 
the  skull  by  passing  through  the  middle  compartment  of  the  jugular 
foramen,  presenting,  immediately  after  its  exit,  an  enlargement  known 
as  the  gangliform  plexus.  The  accessory  portion  of  the  spinal  acces- 
sory nerve  joins  this  ganglion,  while  the  hypoglossal  nerve  winds 
around  it  in  a  spiral  manner. 

As  has  been  previously  stated,  the  immediate  cause  of  the  rhyth- 
mical contractions  of  the  heart  lies  in  the  protoplasm  of  the  muscle-cells 
themselves,  but  that  the  rate  and  force  of  its  beats  are  influenced  by 
impulses  reaching  it  through  the  central  nervous  system.  The  effects 
of  these  impulses  are  twofold :  inhibition,  or  diminution  in  the  rate  or 
force  of  the  heart-beat,  and  acceleration,  or  increase  in  the  rate  or 
force.  Both  the  inhibitory  and  accelerator  centers  are  located  within 
the  medulla,  fibers  from  which  leave  the  cranium  and  reach  the  heart. 
Of  these  efferent  fibers  of  the  vagus,  the  inhibitory  ones  are  most 
prominent  and  come  from  the  spinal  accessory. 

However,  there  are  accelerator  fibers  which  take  their  origin  in 
the  medulla  oblongata  and  then  descend  in  the  spinal  cord,  emerge 
by  the  anterior  roots  to  the  stellate  ganglion  or  first  thoracic,  then  by 
the  annulus  of  Vieussens  to  the  inferior  cervical  ganglion  of  the  sym- 
pathetic, and  then  to  the  heart. 


190  PHYSIOLOGY. 

Knowledge  of  the  presence  of  inhibitory  fibers  in  the  vagus  is 
due  to  the  investigation  of  the  Weber  brothers,  who,  about  fifty  years 
ago,  demonstrated  their  presence  in  the  vagus  of  the  frog.  They 
showed  that  stimulation  of  one  or  both  produces  slowing  or  complete 
stoppage  of  the  beats  of  the  heart.  Stimulation  not  only  inhibits  the 
heart's  action,  but  also  modifies  it  in  that  the  force  of  the  contraction 


Fig.  35.— Cardiac  Plexus  and  Stellate  Ganglion  of  the  Cat.     (LANDOIS.) 

R,  Right.  L,  Left  (X  1  V2).  1,  Vagus.  2',  Cervical  sympathetic  and  in 
the  annulus  of  Vieussens.  2,  Communicating  branches  from  the  middle  cer- 
vical ganglion  and  the  ganglion  stellatum.  2",  Thoracic  sympathetic.  3,  Re- 
current laryngeal.  4,  Depressor  nerve.  5,  Middle  cervical  ganglion.  5',  Com- 
munication between  5  and  the  vagus.  6,  Ganglion  stellatum  (first  thoracic 
ganglion).  7,  Communicating  branches  with  the  vagus.  8,  Nervus  accelerans. 
8,  8',  8",  Roots  of  accelerans.  9,  Bramch  of  ganglion  stellatum. 

and  the  income  and  output  of  the  ventricle  are  diminished.  The  num- 
ber of  ventricular  and  auricular  beats  are  not  in  unison,  the  latter  very 
often  being  more  frequent. 

It  makes  no  difference  whether  one  irritates  the  center  of  the 
pneumogastrics,  their  trunk,  or  peripheral  ends  within  the  heart,  the 
same  result  follows :  there  is  a  diminution  in  the  number  of  the  heart- 
beats. A  tap  upon  the  abdominal  wall  is  able  to  throw  the  pneumo- 


THE  CIRCULATION. 


191 


gastric  into  greatly  increased  action ;  so  that  the  heart  is  often  stopped 
and  death  ensues.  In  this  case  the  sympathetic  nerves  convey  the 
impression  up  the  spinal  cord  to  the  center  of  the  pneumogastric  in 
the  medulla.  From  the  medulla  the  impulse  is  sent  down  the  in- 
hibitory fibers  of  the  pneumogastric,  which  cause  arrest  of  the  heart. 
The  arrest  occurs  always  in  diastole,  never  in  systole. 

All  of  the  sensory  nerves  of  the  body  have  a  reflex  relation  to  the 
pneumogastrics.  Even  pinching  the  skin  of  some  fishes  is  sufficient  to 
stop  the  heart.  Irritation  of  the  branches  of  the  fifth  nerve  in  the 


SM — -, 


GP-Y- 


Fig.  36. — Course  of  Vagus  Nerve  in  Frog.     (STIRLING.) 

SM,  Submentalis.  LU,  Lung.  Y,  Vagus.  OP,  Glosso-pharyngeal.  HQ, 
Hypoglossal.  L,  Laryngeal.  PH,  SH,  OH,  OH,  Petro-,  sterno-,  genio-,  and 
omo-  hyoid.  HO,  Hypoglossus.  H,  Heart.  BR,  Brachial  plexus. 

rabbit  by  ether  and  other  vapors  can  stop  the  heart.     There  are  reasons 
to  believe  similar  results  can  occasionally  be  obtained  in  man. 

SWALLOWING  FLUIDS. — Experimenters  have  demonstrated  that 
swallowing  interferes  with  or  even  may  abolish  for  a  short  time  the 
cardio-inhibitory  action  of  the  v,agus.  By  reason  of  this  the  pulse- 
rate  is  greatly  increased.  Sipping  a  wineglassful  of  water  will  raise 
the  pulse-count  30  per  cent.  In  this  way  water  can  be  made  to  behave 
as  a  powerful  cardiac  excitant.  The  course  of  the  impulse  is  along 
afferent  fibers  of  the  nerves  supplying  the  oesophagus  to  the  cardio- 
inhibitory  center,  whose  tonus  is  reduced. 


19.2 


PHYSIOLOGY. 


Stimulation  of  the  vagus  always  produces  the  same  result — 
inhibition — no  matter  at  what  point  in  its  course  the  nerve  be  stimu- 
lated. 

If  the  pneumogastrics  be  divided  in  the  neck  the  heart  runs  with 
great  rapidity.  This  is  due  to  the  removal  of  the  inhibitory  power, 
which  comes  from  the  center  located  within  the  medulla.  A  brake, 
as  it  were,  is  taken  from  the  heart,  so  that  all  restraint  is  removed. 

Inhibition  is  not  perceived  immediately  after  the  application  of 
the  stimulus.  There  is  present  a  distinct  latent  period  which  pre- 
cedes the  inhibitory  effects.  Various  conditions  may  modify  the 
length  of  this  period,  but  the  average  duration  is  one  or  two  beats. 
The  stimulus  is  applied  to  either  side,  though  the  right  vagus  seems 
to  be  more  susceptible;  when  the  stimulus  is  strong  enough  to  cause 


imm 


Fig.  37.— Tracing  by  Lever  Attached  to  Frog's  Heart  on  Stimula- 
tion of  the  Pneumogastric  Nerve.     (FOSTER.) 

a-b  shows   time   of   stimulation  by   electricity.     As  the   tracing   shows,    the 
heart's  movements  were  arrested  for  some  time. 

complete  stoppage,  this  condition  is  the  result  of  lengthening  the 
diastole,  the  most  usual  occurrence. 

PECULIARITIES. — Some  of  the  points  of  peculiarity  of  the  vagus 
and  its  action  are:  1.  The  heart  is  arrested  in  diastole;  so  that  the 
slowing  depends  upon  the  period  of  diastole.  2.  The  irritation  of  one 
nerve  alone  acts  upon  the  two  sets  of  inhibitory  ganglia  in  the  heart 
by  reason  of  association  fibers.  3.  After  the  arrest  of  the  heart  by 
excitation  of  the  vagus  the  heart  begins  its  contractions  first  in  the 
auricles.  4.  The  inhibitory  fibers  in  the  vagus  come  from  and  repre- 
sent the  accessory  portion  of  the  spinal  accessory. 

Experiments  upon  rabbits  and  other  animals  have  revealed  the 
presence  of  a  nerve  which  is  an  afferent  branch  of  the  vagus ;  that  is, 
impulses  are  carried  along  its  fibers  from  the  heart  to  the  deep  origin 
of  the  vagus  to  be  carried  to  the  main  vasomotor  center.  This  nerve 
is  termed  the  depressor,  and  takes  its  source  partly  from  the  vagus  and 


THE  CIRCULATION. 


193 


partly  from  the  superior  laryngeal  nerve.  After  division,  if  its  distal 
end  be  stimulated  no  effect  is  produced  upon  the  heart;  if,  on  the 
contrary,  the  central  end  be  stimulated,  immediately  the  blood-pressure 
falls,  while  the  heart-beat  is  not  affected.  This  nerve  terminates  in 
the  endocardium.  It  reduces  the  arterial  tension  by  inhibiting  the 
tonus  of  the  vasoconstrictor  center,  which  allows  the  abdominal  vessels 
to  dilate,  which  are  innervated  by  the  greatest  vasoconstrictor  nerve  in 
the  body — the  splanchnic. 

Accelerators. — When  they  are  irritated  they  not  only  accelerate 
the  beat  of  the  heart,  but  also  increase  the  force,  causing  a  greater 
output  of  blood. 

The  accelerators  apparently  have  less  powerful  functions,  for 
when  the  inhibitors  and  they  are  simultaneously  irritated  the  effect 


Fig.  38. — Manometer  Tracing  from  Rabbit,  on  Stimulation  of 

the  Pneumogastric  Nerve.     (FOSTER.) 

a-&  represents  time  of  stimulation. 

is  inhibition.  The  phenomenon  is  less,  however,  than  if  the  same 
inhibitors  had  been  stimulated  by  themselves.  Aside  from  their  great 
and  primary  differences  as  to  the  effects  produced,  the  accelerators  dif- 
fer in  that  they  require  a  greater  intensity  of  stimulus  to  produce  any 
results ;  also  in  that  a  comparatively  long  latent  period  precedes  every 
effect.  In  every  respect  the  accelerators  seem  to  be  directly  opposite  to 
the  inhibitors.  They  are  the  antagonists  of  the  inhibitors. 

When  the  accelerator  fibers  are  divided,  the  rhythm  of  the  heart 
remains  unchanged.  This  proves  that  the  accelerator  center  is  not 
constantly  in  a  state  of  tonic  excitement.  WThen,  however,  the  periph- 
eral ends  of  the  accelerators  are  stimulated  by  a  faradic  current,  the 
heart  becomes  accelerated  in  action. 


194 


PHYSIOLOGY. 


Ludwig  holds  that  the  reduction  of  blood-pressure  in  the  capil- 
laries of  the  brain,  but  particularly  those  of  the  medulla,  excites  the 
accelerators.  Exhilarating  emotions  and  diminished  blood-pressure 
also  throw  them  into  activity.  Oxygen  is  an  accelerator.  When  the 
heart  beats  rapidly  from  any  agreeable  cause,  or  one  feels  "light  at 
heart,"  the  manifestation  is  due  to  the  influence  of  the  accelerator 
fibers  on  the  heart. 

The  sympathetic  fibers  which  pass  to  the  heart  are  nonmedullated, 
having  lost  their  medulla  in  the  various  ganglia  through  which  they 


Fig.  39. — Scheme  of  the  Cardiac  Nerves  in  the  Rabbit. 
(LANDOIS.) 

P,  Pons.  MO,  Medulla  oblongata.  Mag.,  Vagus.  SL,  Superior  laryngeal. 
TL,  Inferior  laryngeal.  SC,  Depressor  or  superior  cardiac  branch.  1L-H, 
Cardio-inhibitory.  H,  Heart,  a,  a,  Accelerator  fibers.  S,  Cervical  sym- 
pathetic. 

pass.  In  this  respect  they  are  in  direct  antagonism  to  the  inhibitory 
fibers,  whose  course  can  be  ascertained  by  the  histologist  in  his  micro- 
scopical anatomy  of  the  pneumogastric.  The  augmentor  center  is  in 
the  medulla  oblongata. 

Thus,  the  heart  is  controlled  by  two  nerves  whose  functions  are 
diametrically  opposite  in  character.  They  establish  a  system  of 
"check"  upon  one  another,  each  normally  preventing  extremes  in  the 
action  of  the  other. 


THE  CIRCULATION. 


195 


Influence  of  Drugs. — Because  of  the  complicated  action  of  various 
drugs  upon  the  heart,  many  observers  are  led  to  believe  that  there  are 
various  internal  mechanisms  of  the  heart  upon  which  these  substances 
act.  Besides  acting  upon  the  muscular  tissue,  some  are  found  which 
exert  influences  upon  the  intracardiac  ganglia.  The  two  drugs  that 
are  most  familiar  to  the  physiologist  and  those  with  which  he  is  most 
engaged  in  performing  his  experiments  are  atropine  and  muscarine. 
Their  actions  are  both  nervous.  Thus,  atropine  paralyzes  the  inhib- 
itory ganglia,  thereby  giving  the  accelerators  full  sway,  the  consequence 
being  augmentation  of  the  heart's  beats.  On  the  other  hand,  mus- 
carine stimulates  permanently  the  inhibitory  ganglia,  so  that  the  heart- 


JL  UUUL  JULJUlJ1. 


Fig.  40.  —  Blood-pressure  Tracing  Obtained  by  Stimulating  the 

Depressor  Nerve  in  a  Rabbit.     (  FOSTER.) 
C-O  represents  time  of  stimulation.     T  represents  seconds. 

beats  are  slowed,  or,  if  the  dose  be  large  enough,  complete  arrest  of 
heart  movement  follows. 

If  a  frog's  heart  be  excised  and  placed  in  a  suitable  vessel  with 
a  few  drops  of  a  very  dilute  solution  of  muscarine  placed  upon  it, 
its  beats  soon  cease  and  will  continue  quiescent  as  long  as  the  mus- 
carine remains  upon  it.  When  the  muscarine  is  removed  and  atropine 
applied  to  the  heart,  its  regular  beats  manifest  themselves  within  a 
short  time. 

Some  drugs  produce  results  by  their  effects  upon  the  heart-muscle 
alone,  either  stimulating  or  depressing  the  same.  Thus,  the  muscular 
contractions  are  rendered  more  forceful  while  the  rate  is  uninfluenced 
by  the  action  of  digitalis,  strophanthus,  etc.  The  muscular  contrac- 
tions are  depressed  by  veratrum,  aconite,  etc. 


196  PHYSIOLOGY. 

In  addition  to  drugs  influencing  the  heart's  action  by  effects  upon 
its  muscle  and  ganglionic  nerve  terminations,  some  exert  an  influence 
upon  the  vagus  center  in  the  medulla  oblongata.  Thus,  aconite,  digi- 
talis, and  adrenalin,  by  stimulating  this  center,  produce  a  slowing  of 
the  heart-beats. 

Some  heart-poisons  in  small  doses  diminish  the  heart's  action  and 
in  large  doses  usually  accelerate  its  movements ;  or  the  reverse  may 
be  the  truth  with  regard  to  the  doses  of  other  drugs. 

Effect  of  Stimuli. — If  in  a  frog's  heart  the  Stannius  ligature  be 
applied  around  the  heart  at  the  junction  of  the  sinus  with  the  auricle, 
the  auricle  and  ventricle  stand  still  in  diastole.  If  now  to  this  heart 
a  series  of  slow  induction  shocks  be  applied,  it  will  be  found  that  after 
the  first  contraction  there  is  a  gradual  increase  in  the  height  of  the 
contraction,  making  what  is  called  the  staircase  phenomenon  of  Bow- 
ditch.  Although  the  strength  of  the  electrical  current  was  the  same, 
yet  it  seems  that  the  heart  by  its  own  contraction  increases  its  excita- 
bility. With  a  weak  induction  current  the  apex  produces  as  strong  a 
contraction  as  a  strong  current  would  do.  That  is,  a  weak  induction 
current  either  does  not  produce  a  contraction  or,  if  it  does,  it  is  the 
very  best  it  can  do.  It  is  all  or  nothing  for  the  heart's  contractions. 
In  this  staircase  of  beats  each  contraction,  although  maximal  inasmuch 
as  it  is  the  full  effect  of  which  the  muscle  is  then  capable,  is  a  little 
greater  than  the  preceding  contraction. 

Nutrition  of  Frog's  Heart. — For  the  heart  to  continue  beating  it 
must  be  fed.  To  do  this  a  liquid  is  perfused  through  the  cavity  of  the 
frog's  heart.  This  liquid  must  contain  a  right  proportion  of  sodium 
chloride,  calcium  salt,  and  a  potassium  salt.  If  the  solution  of  sodium 
chloride,  potassium  chloride,  or  calcium  chloride,  with  sodium  bicar- 
bonate in  distilled  water,  is  charged  with  oxygen  it  will  keep  an 
excised  rabbit's  heart  beating  for  twelve  hours.  The  presence  of 
proteid  in  it  does  not  seem  necessary. 

THE   ARTERIES. 

All  vessels  leaving  the  heart  are  arteries.  From  it  proceed  the 
aorta  and  pulmonary  artery,  the  former  from  the  left,  the  latter  from 
the  right  ventricle.  All  of  the  branches  of  the  arteries  continue  to 
divide  to  form  smaller  arteries,  these  in  turn  become  arterioles,  which 
are  followed  by  capillaries  (hairlike  vessels).  To  cause  as  little  fric- 
tion as  possible  the  branches  are  almost  uniformly  given  off  at  an 
acute  angle;  the  total  area  of  the  cross-sections  of  the  branches  is 
usually  greater  than  the  sectional  area  of  the  original  trunk  from 


THE  CIRCULATION.  197 

which  sprung  the  branches.  As  the  distance  from  the  source  is  in- 
creased the  area  supplied  by  the  branches  is  increased  also,  giving 
the  general  impression  of  a  cone  in  its  contour;  its  base  is  outlined 
by  the  capillaries,  its  apex  being  represented  by  the  point  from  which 
the  branch  springs  from  the  parent  trunk. 

The  pulmonary  artery  arises  from  the  right  ventricle  in  front  of 
the  origin  of  the  aorta  under  whose  arch  it  very  shortly  passes,  then 
to  divide  into  two  main  branches,  one  for  each  lung.  Within  the 
lung-substance  they  divide  and  subdivide  very  rapidly  to  form  numer- 
ous capillaries  whereby  the  blood  may  become  thoroughly  oxidized. 

Because  of  the  considerable  amount  of  muscular  and  elastic  fibers 
present  in  the  walls  of  the  arteries,  they  (unlike  veins)  are  usually 
found  empty  and  dilated  after  death. 

Arterial  Structure. — The  walls  of  the  arteries  are  composed  of 
three  coats :  an  internal  one  of  endothelial  nature,  the  tunica  Mima; 
a  middle  coat  of  muscular  fibers,  tunica  media;  and  an  external, 
cellular  coat,  tunica  adventitia. 

TUXICA  INTIMA. — The  tunica  intima  of  the  arteries  is  the  thin- 
nest coat  and  the  most  transparent  and  elastic.  These  properties 
permit  the  caliber  of  the  artery  to  be  enlarged  without  any  great 
danger  of  rupturing  its  walls.  It  is  composed  of  three  different  struc- 
tures: (1)  an  epithelial  layer,  the  endothelium,  which  consists  of 
elliptical  cells;  (2)  a  subepithelial  layer,  which  is  composed  of  con- 
nective tissue  with  branched  cells;  (3)  an  elastic  layer. 

By  reason  of  its  smooth  surface  there  is  very  little  friction  in  the 
rush  of  the  blood-current. 

TUNICA  MEDIA. — It  is  composed  of  two  varieties  of  tissue:  (1) 
muscular  and  (2)  elastic. 

The  unstriped  muscular  fibers  run  in  a  circular  direction  around 
the  vessels.  In  the  large  arteries  there  is  a  predominance  of  elastic 
tissue ;  in  the  arterioles  there  is  no  elastic,  but  muscular  tissue.  The 
contractility  of  the  arteries  depends  upon  the  muscular  tissue.  Where 
there  is  an  excess  of  elastic  tissue  there  is  very  little  muscular  tissue 
in  the  blood-vessel,  and  where  the  elastic  tissue  is  at  a  minimum  there 
is  a  maximum  of,  muscular  tissue. 

TUNICA  ADVENTITIA. — This  coat  is  composed  of  bundles  of  con- 
nective tissue  with  some  elastic  tissue. 

VASA  VASORUM. — Like  every  other  tissue,  the  wall  of  the  vessels 
needs  nutritive  supplies.  This  is  furnished  by  small  capillaries  which 
run  only  in  the  tunica  adventitia  of  the  blood-vessel.  To  these  vessels 
has  been  given  the  name  of  vasa  vasorum. 


198  PHYSIOLOGY. 

VEINS. 

Like  the  arteries,  veins  are  branching  tubes ;  but  they  are  larger, 
more  numerous,  and  as  a  consequence  have  more  capacity  to  hold 
blood.  Veins  have  their  beginning  in  the  capillary  vessels  and  by 
gradually  uniting  form  themselves.  These  small  veins  unite  to  form 
larger  ones,  the  venae  cavas,  which  empty  into  the  right  auricle.  The 
veins  have  about  three  times  the  capacity  of  the  arteries.  The  veins 
consist  of  a  superficial  and  deep  set,  the  former  not  associated  with  the 
arteries  and  being  subcutaneous,  the  deep  set  usually  running  along 
the  side  of  the  artery  and  hence  called  venae  comites.  Anastomoses 
between  the  veins  of  the  large  size  are  more  frequent  than  in  the  corre- 
sponding arteries.  The  veins,  like  the  arteries,  have  an  external,  a 
middle,  and  an  internal  coat.  The  coats  of  the  veins  are  much  thinner 
than  arteries,  and  when  divided  collapse,  while  the  artery,  divided, 
stands  open.  The  walls  of  the  veins  are  inelastic,  because  they  have 
no  elastic  tissue. 

Valves. — The  chief  feature  of  the  veins  are  the  valves,  which  are 
so  arranged  as  to  prevent  the  blood  from  flowing  backward.  The 
valves  ordinarily  are  in  pairs  opposite  each  other  and  are  formed  of 
crescent-shaped  doublings  of  the  lining  membrane  of  the  veins,  with 
some  interposed  nbro-elastic  tissue.  The  valves  are  directed  toward 
the  heart.  If  a  vein  is  compressed  the  blood  is  driven  back  and  presses 
the  valves  inward  and  closes  the  vein.  The  pulmonary  veins  contain 
no  valves,  and  the  same  may  be  said  for  the  superior  and  inferior 
venae  cavse,  the  portal  vein,  and  most  of  those  of  the  head  and  neck. 
The  veins  of  the  lower  extremities  contain  more  valves  than  the  corre- 
sponding vessels  of  the  upper  extremity.  In  certain  organs  channels 
are  seen, lined  with  an  extension  of  the  internal  coat  of  the  vein,  which 
are  called  venous  sinuses,  as  in  the  dura  mater  and  uterus.  Vasa 
vasorum  are  also  distributed  to  the  veins.  In  the  coats  of  both  arteries 
and  veins  are  lymph-spaces. 

The  nerve-supply  to  the  arteries  is  liberal,  to  the  veins  much  less 
so.  The  supply  is  derived  chiefly  from  the  sympathetic  system,  with 
a  few  filaments  from  the  cerebro-spinal  system.  Upon  the  larger 
vessels  these  nerves  form  plexuses  with  ganglia  at  frequent  intervals. 

THE   CAPILLARIES. 

The  smallest  arteries  suddenly  divide  into  an  extremely  fine  net- 
work of  hairlike  tubes,  the  capillaries.  These  furnish  the  connecting 
link  between  arteries  and  the  beginnings  of  veins.  They  serve  as  this 
intermediate  agent  in  all  structures,  between  the  arteries  and  the  veins. 


THE  CIRCULATION.  199 

Each  capillary  tube  is  from  1/200o  to  Vsooo  inch  in  diameter,  while 
it  averages  1/80  inch  in  length. 

Capillaries  are  composed  of  the  same  kind  of  endothelial  cells 
that  the  intima  of  the  arteries  is;  in  fact,  the  capillaries  seem  to  be 
the  prolongations  of  the  lining  of  the  arteries.  Their  walls  are  made 
up  of  a  single  layer  of  lance-shaped  endothelial  cells.  In  the  wall  of 
the  capillary  between  the  cells  we  find  the  cement-substance  which 
permits  the  blood-corpuscles  to  penetrate  it  in  diapedesis.  These 
little  vessels  penetrate  the  spaces  between  the  cells  of  the  tissues  in 
such  a  fine  network  that  many  of  the  cells  are  in  contact  with  several 
vessels.  So  closely  arranged  are  they  that  the  point  of  a  very  fine 
needle  cannot  enter  the  skin  without  injuring  some  of  them.  The 
total  capacity  of  the  capillaries  is  about  three  hundred  times  that  of 
the  arteries,  so  that  in  them  much  of  the  blood-pressure  is  lost,  but 
normally  there  always  remains  sufficient  to  maintain  a  steady  move- 
ment. 

THE  CIRCULATION  OF  THE   BLOOD. 

The  physicians  and  naturalists  of  antiquity,  even  at  the  epoch 
when  they  were  permitted  to  get  enlightenment  from  anatomy,  re- 
mained in  ignorance  of  the  circulatory  movement  of  the  blood.  The 
circulatory  apparatus  is  not  one  of  those  the  mere  inspection  of  which 
could  reveal  its  function;  in  fact,  when  viewed  in  a  cadaver  illusions 
are  very  apt  to  rise.  In  it  the  arteries  are  empty  and  show  a  gaping 
cavity  when  incised,  so  that  they  were  thought  to  contain  air  or  some 
subtle  spirit,  the  latter  taking  its  origin  in  the  ventricles  of  the  brain 
to,  in  some  unaccountable  manner,  reach  the  circulatory  system.  To 
them  the  name  artery  was  given,  since  the  veins  alone  were  believed  to 
be  the  true  blood-vessels.  Such  was  the  opinion  entertained  by  men 
who  lived  in  the  fourth  and  fifth  centuries  before  the  Christian  era. 

In  the  second  century  of  our  era  Galen  discovered,  by  means  of 
vivisections,  that  the  arteries  contain  blood.  He  even  admitted  that 
the  arteries  communicated  with  the  veins.  But,  as  if  to  pay  his  debt 
to  error,  he  professed  that  the  two  hearts  are  in  communication  with 
one  another  through  numerous  apertures  which  riddle  the  septum 
which  separates  the  two.  For  nearly  fourteen  centuries  the  opinions 
of  Galen  had  inviolate  authority,  when  it  was  finally  ascertained  by 
Vesalius  that  the  separating  septum  was  not  perforated.  It  was 
Michael  Servetus  who,  in  a  theological  work,  clearly  pointed  out  the 
passage  of  the  blood  from  the  right  heart  to  the  left  through  the  pul- 
monary Hood-vessels.  His  system  was  true,  but  not  based  upon  ex- 
periment, since  he  knew  nothing  of  the  heart's  force  and  valves. 


200  '  PHYSIOLOGY. 

In  was  in  1628  that  William  Harvey  published  his  immortal 
discovery  of  the  circulation  of  the  blood.  True,  a  great  deal  had 
been  suspected  and  there  abounded  a  perfect  chaos  of  confused  and 
scattered  facts.  He  established  by  numerous  and  admirably  inter- 
preted experiments  his  doctrine  of  the  two  circulations:  great  and 
small. 

To-day  it  would  be  superfluous  to  recall  all  of  the  arguments 
which  Harvey  had  to  make  use  of  to  prop  up  that  doctrine.  There- 
fore there  will  be  stated  here  only  some  of  his  experimental  proofs,  the 
interpretation  of  which  appear  easy  to  us  in  the  light  of  our  present 
knowledge. 

When  an  artery  is  opened,  said  Harvey,  the  blood  issues  in 
unequal  jerks,  alternately  weaker  and  stronger.  The  stronger  coin- 
cides with  diastole  of  the  artery  and  consequently  with  ventricular 
systole.  Also,  if  an  artery  of  a  living  animal  be  cut  across,  the  blood 
continues  to  gush  by  jerks  from  that  end  of  the  vessel  still  in  com- 
munication with  the  heart,  whereas  it  soon  ceases  to  flow  from  that 
severed  end  which  is  more  remote  from  the  central  organ. 

When  the  arm  is  bound,  as  for  bleeding,  the  veins  swell  up  below 
the  ligature  to  become  knotty  on  a  level  with  their  valves.  If  force  be 
attempted  to  press  the  blood  away  from  the  heart,  the  knots  become 
more  marked;  on  the  contrary,  if  the  blood  be  pressed  toward  the 
heart,  it  passes  freely.  From  this  Harvey  deducted  that  the  direction 
of  the  venous  blood  is  from  the  periphery  to  the  heart. 

When  an  artery  is  obstructed,  the  blood  accumulates  between  the 
heart  and  the  obstacle;  on  the  contrary,  the  accumulation  in  the  case 
of  a  vein  is  between  the  obstructed  point  and  the  general  capillaries. 
In  the  arteries,  therefore,  the  blood  flows  from  the  heart  to  the  ex- 
tremities; in  the  veins,  from  the  extremities  toward  the  heart. 

If  an  artery  be  completely  severed  and  the  animal's  blood  be  per- 
mitted to  flow,  all  of  its  blood  will  eventually  pass  through  the  opening. 
Would  this  occur  if  there  were  not  a  continual  passage  of  the  blood 
from  the  heart  to  the  arteries,  then  to  the  veins,  and  finally  to  the 
heart  again;  that  is  to  say,  a  true  circulation? 

This  great  physiologist  also  observed  that  if  poison  be  injected  at 
but  a  single  point  there  will  follow  a  general  constitutional  disturb- 
ance, explained  only  by  the  movement  of  this  vital  fluid  throughout 
the  entire  body. 

To  be  able  to  ascertain  by  vision  the  direct  passage  of  the  blood 
from  the  arteries  into  th~e  veins  was  not  allowed  Harvey.  It  was  left 
to  Malpighi,  who,  in  1661,  while  examining  the  lung  and  mesentery 


THE  CIRCULATION. 


201 


of  a  frog  with  the  aid  of  a  micro- 
scope, was  able  to  note  the  circu- 
lation of  the  blood  in  the  capil- 
lary blood-vessels.  The  spectacle 
of  capillary  circulation  within 
the  web  of  a  frog's  foot  or  tail  of 
a  tadpole  is  within  the  reach  of 
every  student.  Harvey  was  de- 
nied this  from  lack  of  lenses  pow- 
erful enough  to  demonstrate  it. 

Now  that  the  general  plan 
of  the  circulation  has  been  noted, 
attention  is  naturally  turned 
toward  the  principles  governing 
the  flow  of  the  blood.  The  me- 
chanical act  of  impulsion  can  be 
readily  imitated  by  physical  ap- 
paratus, but  physics  do  not  ac- 
count for  a  certain  part  of  the 
body  receiving  blood,  now  more, 
now  less,  abundantly;  becoming 
congested  or  pale,  warm  or  cold; 
and  at  the  same  time  the  impetus 
remaining  perceptibly  the  same. 

By  employing  a  simple  piece 
of  apparatus,  designed  by  E.  H. 
Weber,  the  main,  simple,  physical 
phenomena  of  the  circulation 
may  be  simulated.  To  imitate 
the  Harveian  circuit,  take  a  piece 
of  small  intestine,  sufficiently 
long,  joining  the  two  ends  so  that 
there  is  formed  a  closed  and  cir- 
cular conduit.  A  part  of  this 
elastic  conduit  is  limited  by  two 
valves  which  open  according  to 
the  direction  it  is  desired  that  the 
current  of  liquid  should  go.  The 
arrangement  of  the  valves  is  such 
that  all  backward  flow  is  pre- 
vented. On  filling  the  apparatus 


Fig.  41.— Weber's  Schema. 

4-5  and  8-9  are  two  pieces  of  intestine  of  the 
same  size.  6,  A  piece  of  glass  tubing.  11  and  2, 
Two  wooden  tubes.  1,  A  short  piece  of  intestine. 
3,  12,  Valves  which  open  only  in  one  direction. 
1  represents  the  ventricle.  10,  A  funnel  to  let 
water  enter  the  schema.  4-5,  The  arterial  sys- 
tem. 8-9,  The  venous  system.  7,  A  sponge  rep- 
resenting the  capillaries.  3,  The  semilunar 
valve.  12,  The  auriculo-ventricular  valve. 


202  PHYSIOLOGY. 

with  water  by  means  of  a  funnel,  it  is  ready  for  operation.  When  any 
portion  of  this  elastic  conduit  is  squeezed  the  liquid  immediately 
beneath  the  point  of  pressure  attempts  to  escape.  This  it  can  do 
only  in  one  direction  (because  of  the  valves),  thereby  producing  a 
forward  motion  of  the  liquid.  With  each  compression  there  follows  a 
corresponding  wave,  so  that  if  the  compressions  be  numerous  enough 
the  liquid  will  move  round  and  round  within  the  conduit.  This 
represents  only  very  imperfectly  the  circulation  of  the  blood;  in  the 
living  apparatus  the  impulse  of  the  heart  is  not  at  the  end  of  the 
venous  system. 

From  the  operation  of.  even  so  simple  a  piece  of  apparatus,  it 
cannot  but  be  noticed  that  the  circulation  depends  upon  a  differ- 
ence of  tension.  Liquids  always  take  the  direction  of  the  pressure. 
The  obstruction  offered  to  the  blood  in  the  presence  of  the  capillaries 
has  a  tendency  to  increase  arterial  tension  at  the  expense  of  venous 
pressure.  The  narrower  and  more  difficult  the  capillaries  to  be  tra- 
versed are,  the  greater  is  arterial  pressure,  or  vice  versa.  The  prime 
cause  of  difference  of  pressure  is  ventricular  contraction,  aided,  how- 
ever, by  elasticity  of  vessels. 

CIRCULATION  IN  THE  BLOOD=VESSELS. 

This  field  of  physiology  presents  problems  of  a  physical  nature,  in 
that  the  flow  of  the  liquid,  blood,  is  through  tubes.  But  it  must  be 
remembered  that  the  tubes  employed  in  the  circulation  are  living, 
more  or  less  elastic  ones,  and  that  physical  laws  are  correspondingly 
altered. 

The  analogy  between  the  nervous  system  and  the  telegraphic  sys- 
tem is  a  very  striking  one,  and  is  much  used  by  physiologists  and 
others.  -Even  more  forceful  is  the  analogy  between  the  circulatory 
system  and  the  system  of  water-supply  of  a  town  or  city,  except  that 
there  is  no  return  of  the  latter's  fluid  to  the  starting-place.  The  water 
starts  upon  its  flow  from  the  elevated  reservoir  to  pass  through  large 
mains  at  first  and  is  distributed  through  branches  that  become  smaller 
and  smaller  as  they  subdivide  on  their  way  to  different  houses.  Like- 
wise, the -blood  starts  from  the  centrally  located,  pumping  heart, 
passes  through  large  trunks  at  first,  to  be  distributed  through  branches 
that  become  smaller  and  smaller  as  they  subdivide  on  their  way  to 
different  tissues.  In  short,  the  physical  laws  of  the  circulation  are 
the  modified  physical  laws  of  the  flow  of  liquids  through  tubes.  From 
this  it  will  be  readily  deduced  that  a  competent  knowledge  of  the 
laws  of  circulation  must  be  preceded  by  some  knowledge  of  physical 


THE  CIRCULATION.  203 

laws.  These  will  be  referred  to  from  time  to  time  in  the  treatment 
of  the  present  subject. 

The  flow  of  liquid  is  caused  by  a  difference  of  pressure  between 
the  different  parts  of  a  mass  of  liquid.  The  attraction  of  the  earth 
( gravitation)  provides  a  continuous  pressure  which  will  produce  a 
flow  of  liquid  along  channels  or  through  tubes,  provided  the  source  be 
elevated  and  the  outlet  low. 

The  circulation  through  the  heart-vessels  is  also  caused  by  a 
difference  in  pressure  due  to  the  primary  propelling  force  of  the  heart- 
action.  That  is,  the  pressure  in  it  exceeds  that  of  the  arteries;  the 
latter's  pressure,  kept  high  by  the  heart's  force  and  peripheral  re- 
sistance, is  greater  than  that  in  the  capillaries.  Though  that  exerted 
in  the  capillaries  is  small,  it  is  yet  in  excess  of  that  existing  in  the 
veins.  The  lowest  pressure  is  found  in  the  blood  about  to  enter  the 
heart  after  having  first  made  its  circuit  through  the  Body-tissues. 
The  direction  of  the  flow  of  any  liquid  is  always  from  the  higher 
pressure  toward  the  lower ;  therefore  the  flow  of  blood  within  the  body 
is  from  the  heart  around  through  the  body  back  to  the  heart  again; 
that  is,  it  circulates. 

ELASTICITY   OF   THE   ARTERIES. 

It  is  known  that  the  blood  is  sent  out  by  the  heart  in  an  inter- 
mittent manner,  each  contraction  of  the  ventricle  pushing  a  mass,  as 
the  stroke  of  the  piston  of  a  force-pump  would  do.  If,  however,  the 
movement  of  the  blood  in  the  capillaries  is  observed  with  a  micro- 
scope it  is  ascertained  that  in  the .  normal  state  it  is  perfectly  con- 
tinuous. The  movement  of  blood  has  been  transformed  in  its  course 
from  the  heart  to  the  extremities.  This  transformation  of  the  move- 
ment is  due  to  the  elasticity  of  the  arteries.  Hydraulics  had  ascer- 
tained this  remarkable  effect  of  elasticity  in  fire  engines,  for  example ; 
the  water  from  the  machine  is  rendered  less  jerky  by  running  liquid 
under  a  bell  filled  with  air;  the  elastic  force  of  the  gas  thus  com- 
pressed transforms  the  brief  and  intermittent  impulsion  of  the  stroke 
to  a  continuous  stream. 

Intermittent  Afflux  Apparatus. — Marey  has  experimentally  dem- 
onstrated that,  in  the  case  of  intermittent  afflux  of  liquid  in  a  conduit 
of  a  given  caliber,  the  elasticity  of  that  conduit  increases  the  quantity 
of  the  liquid  that  can  penetrate  there  under  a  given  pressure. 

Suppose  a  force-pump,  from  which  runs  a  tube  furnished  with  a 
stop-cock;  a  tube  which  bifurcates  a.t  a  point  to  be  continued  by  two 
conduits  of  the  same  caliber.  One  of  these  is  made  with  elastic  walls 


204  PHYSIOLOGY. 

(C)f  the  other  with  rigid  walls  (B).  A  valve  placed  in  the  elastic 
tube  prevents  the  liquid  from  flowing  back  from  the  tube,  but  offers  no 
obstacle  to  its  direct  current.  Two  lips  of  the  same  caliber  are  fitted 
to  the  ends  of  the  two  tubes. 

When  the  stop-cock  is  opened  and  the  outflow  is  permitted  to  es- 
tablish itself  in  a  continuous  manner,  both  the  rigid  and  elastic  tubes 
pour  out  the  same  quantity  of  liquid.  If,  on  the  contrary,  the  stop- 
cock be  opened  and  shut  alternately  so  as  to  produce  an  intermittent 
access  of  the  liquid,  the  outflow  is  greater  through  the  elastic  tube  than 
through  the  rigid  tube. 

The  blood-circulation  being  of  the  intermittent  afflux  order,  the 
arterial  elasticity  is  favorable  to  the  entrance  of  the  blood  thrown  off 
by  the  heart.  By  the  vessel  elasticity  there  is  produced  a  diminution 


Fig.  42. — Marey's  Intermittent  Afflux  Apparatus.     (LAHOUSSE.) 
A,  Force-pump.     B,  Tube  with  rigid  walls.     C,  Tube  with  elastic  walls. 

of  the  resistance  the  liquid  meets  with.  The  so-called  "friction"  will 
be  much  slighter;  so  that  the  heart  will  be  able  to  send  out  from  its 
ventricles  a  great  quantity  of  blood  with  much  less  expenditure  of 
force. 

The  circulation  in  the  arteries  is  under  the  dependence  of  two 
very  important  properties  of  these  vessels :  elasticity  and  contractility. 
The  nature  of  the  movement  of  the  blood  has,  therefore,  been  trans- 
formed in  its  course  from  the  heart  to  the  extremities.  It  is  now 
known  that  this  transformation  is  due  in  the  main  to  the  elasticity  of 
the  arteries. 

Each  new  entrance  of  the  blood  into  the  arterial  system  must 
necessarily  be  accompanied  with  a  dilatation  of  the  whole  vascular  tree. 
As  soon  as  the  three  ounces  of  blood  which  has  been  ejected  from  the 
left  ventricle  has  penetrated  into  the  aorta,  as  it  flows  through  the 


THE  CIRCULATION.  205 

capillary  system  there  results  a  contraction  of  the  whole  arterial  sys- 
tem until  the  moment  when  a  new  output  of  blood  arrives. 

It  has  been  ascertained  experimentally  that  the  arterial  vessels 
are  much  more  elastic  in  the  direction  of  their  axis  than  in  their 
transverse  diameter.  It  is  in  the  former  direction  then  that  increased 
capacity  of  the  arteries  will  especially  occur.  When  the  trunks  of 
the  arteries  are  of  considerable  extent  the  elongation  may  become 
apparent  to  the  naked  eye,  as  in  the  temporal  artery,  while  there  will 
not  seem  to  exist  any  increase  in  the  transverse  direction  of  the  same 
vessel. 

According  to  Weber,  the  principal  role  of  arterial  elasticity  is  to 
establish,  between  the  arterial  and  venous  tensions,  a  difference  which 
is  indispensable  to  the  movement  of  the  liquid  within  the  circulatory 
apparatus.  In  addition,  the  uses  of  vascular  elasticity  may  be  said  to 
be  twofold :  On  the  one  hand,  it  saves  the  heart  a  considerable  display 
of  force ;  on  the  other,  it  furnishes  the  small  vessels  with  a  continuous 
and  constant  flow  of  blood. 

Next  in  importance  to  the  elasticity  of  the  vessels  is  the  power  of 
contractility,,  by  which  the  caliber  of  a  vessel  is  changed  and  the  supply 
of  blood  to  any  part  or  organ  of  the  body  altered.  This  property 
co-operates  with  elasticity,  so  that  the  lumen  of  any  given  vessel  is 
proportionate  to  the  pressure  exerted.  Were  it  otherwise,  at  some 
times  the  pressure  would  be  too  small,  at  other  times  too  great,  for 
the  quantity  of  inclosed  blood.  The  power  of  contractility  is  very 
prominent  in  the  small  arteries. 

THE  PULSE. 

At  each  ventricular  systole  the  ventricular  contents  are  forced 
into  the  arterial  system,  but,  because  of  the  high  peripheral  tension, 
they  are  unable  to  pass  along  as  a  unit.  In  fact,  the  artery  just 
beyond  the  heart  becomes  distended  because  of  this  influx,  but  by 
virtue  of  its  elasticity  strives  to  regain  its  normal  caliber,  thereby 
giving  to  the  blood  some  motion.  The  main  impetus  to  the  blood  is 
given  by  the  succeeding  systoles,  until  the  smaller  arteries  are  reached, 
when  the  vascular  elasticity  asserts  itself  more,  and  so  helps  along  the 
blood-stream.  By  this  means  is  the  blood  caused  to  circulate.  If  the 
vessels  were  inelastic,  just  as  much  blood  would  be  forced  out  of  the 
veins  into  the  heart  again  as  the  heart  at  each  beat  injects  into  the 
arteries.  Though  the  blood  in  the  elastic  vessels  of  the  body  cannot 
move  freely  as  in  the  inelastic  tubes,  yet  there  is  propagated  at  each 
ventricular  systole  a  wave  which  runs  to  the  periphery  of  the  body. 


206  PHYSIOLOGY. 

This  wave  is  not  an  actual  movement  of  the  particles  of  the  blood,  but 
a  transmission  of  the  impulsion  of  the  heart  throughout,  the  length  of 
the  arterial  tree.  To  this  wave  has  been  given  the  name  pulse.  This 
impulsion  moves  very  swiftly  without  the  liquid  itself  participating  in 
that  swiftness.  This  wave  travels  28  l/2  feet  per  second.  When  a 
systole  of  the  heart  is  revealed  by  a  beating  of  the  radial  artery,  there 
is  not,  at  that  moment,  under  one's  finger  a  single  drop  of  the  blood 
thrown  off  by  the  last  systole.  There  is  only  the  movement  of  that 
blood  which  is  transmitted  by  the  continuity  of  the  liquid.  The 
pulse  may  be  compared  to  a  wave  produced  by  throwing  a  stone  into 
a  pond. 

The  three  factors  concerned  in  the  production  of  the  pulse  are: 
(1)  the  action  of  the  heart,  (2)  the  elasticity  of  the  large  vessels,  and 
(3)  the  resistance  of  the  smaller  arteries  and  the  capillaries. 

The  pulse  is  really  a  shock,  perceptible  to  the  touch  at  each  in- 
crease of  the  arterial  tension,  and  produced  by  successive  affluxes  of  the 
blood  which  the  heart  throws  off. 

In  order  to  perceive  that  shock,  the  vessel  must  be  pressed  by  the 
finger  so  as  to  make  it  lose  its  cylindrical  form  at  that  point.  By 
reason  of  the  dilatation  of  the  vessel,  the  finger  is  raised  at  that  point. 
That  is,  one  perceives  the  pulse.  As  there  may  exist  various  changes 
in  the  arterial  tension,  so  there  may  be  various  types  of  pulse.  Varia- 
tions are,  for  the  most  part,  pathological,  and  so  may  be  considered 
to  be  outside  of  the  domain  of  physiology. 

When  the  physician  feels  the  patient's  pulse  he  gains  valuable 
information  as  to  the  condition  of  the  heart  and  vessels.  The  exam- 
ination of  the  characters  of  the  pulse  is  usually  confined  to  that  por- 
tion of  the  radial  artery  which  lies  in  the  wrist.  Here  the  artery  is 
covered  only  by  skin  and  subcutaneous  tissue,  while  in  addition  the 
shaft  of  the  radius  forms  a  bony  support  against  which  the  artery  may 
be  compressed  by  the  fingers.  From  the  pulse  are  noted  the  following 
points :  Force,  rate,  and  fullness. 

WThile  such  main  features  of  the  pulse  were  able  to  be  depicted 
by  experienced  finger-tips,  it  was  felt  that  there  was  still  very  con- 
siderable that  the  pulse  told  could  it  but  be  translated. 

Everyone  has  seen  the  movements  produced  in  a  limb  by  reason  of 
the  pulsations  of  the  popliteal  artery,  when  one  leg  is  kept  crossed 
over  the  knee  of  the  other.  The  leg  in  this  position  represents 
typically  a  lever  of  the  third  class. 

One  observer  conceived  the  idea  from  this  phenomenon  that  the 
pulse  can  be  very  accurately  studied  by  using  a  very  light  lever  so 


THE  CIECULATION.  207 

attached  that  it  will  oscillate  at  each  heart-beat.  By  virtue  of  a  large 
arm  to  the  lever  the  amplitude  of  the  oscillations  are  so  exaggerated 
that  they  can  be  readily  seen  by  the  naked  eye*  and  their  movements 
graphically  depicted  upon  smoked  papers.  The  instrument  capable 
of  determining  the  various  elements  of  the  pulse  and  so  depicting  them 
that  they  can  be  studied  at  leisure  has  received  the  name  sphygmo- 
graph. 

The  Sphygmograph. — The  name  whereby  this  instrument  is 
known  is  derived  from  two  Greek  words  which  mean  "to  write  the 
pulse."  It  does  write,  for  to-day  graphic  records  of  the  various  fea- 
tures of  the  pulse  are  obtained  by  its  use. 

The  essential  feature  of  this  instrument  is  its  system  of  compound 
levers  whereby  the  initial  motion  is  multiplied  about  fifty  times.  The 


Fig.  43. — Marey's  Sphygmograph.     (Yso.) 

The  parts  B,  B,  B  are  fastened  to  the  wrist  by  the  straps  B,  B.  The 
remaining  part  of  the  instrument  rests  on  the  forearm.  The  end  of  the  screw, 
V,  rests  on  the  spring,  R,  the  button  of  which  lies  on  the  radial  artery.  Any 
movement  of  the  button  at  R  is  communicated  to  V,  which  moves  the  lever, 
L,  up  and  down.  When  in  position  the  blackened  slip  of  glass  is  made  to 
move  evenly  by  the  clockwork,  H,  so  that  records  the  movements  of  the 
lever. 

foot  of  these  levers  rests  upon  the  skin  over  the  artery  whose  tracing  is 
to  be  taken.  Motion  is  transmitted  from  it  to  the  other  end  of  the 
levers,  where  is  inserted  a  recording  needle. 

The  second  feature  of  the  apparatus  is  the  recording  instrument, 
composed  of  clock-work,  which  revolves  a  pair  of  small  cylinders 
between  which  is  moved  a  ribbon  of  blackened  paper.  The  recording- 
needle's  point  rests  upon  this  paper,  correctly  depicting  there  the 
various  features  of  the  pulse. 

In  addition,  each  instrument  is  provided  with  an  apparatus  by 
adjustment  of  which  the  pressure  is  so  regulated  that  the  best  record 
may  be  obtained.  The  graphic  record,  or  pulse-tracing,  is  known  as 
the  sphygmogram. 

The  main  features  of  the  sphygmographic  record  are  an  abrupt 
ascent  with  a  descent  that  is  more  gradual  and  wavy,  representing  the 


208  PHYSIOLOGY. 

rise  and  fall  in  pressure  due  to  ventricular  systole  and  diastole.  The 
wavy  appearance  of  the  downstroke  is  due  to  the  elastic  recoil  being 
more  constant  and  of  longer  duration  than  the  ventricular  systole. 
The  sudden  upstroke  represents  very  forcibly  the  sudden  influx  of 
blood  into  the  aorta  during  systole,  while  the  more  gradual  down- 
stroke  represents  the  slower  fall  of  arterial  pressure  during  diastole. 

The  line  of  ascent  represents  the  dilatation  of  the  artery  by  ven- 
tricular s}rstole  when  the  semilunar  valves  are  forced  open  and  the 
contents  are  projected  into  the  artery.  The  top  of  the  primary  wave  is 
pointed  normally ;  so  has  received  the  term  apex. 

The  more  gradual  downstroke  is  interrupted  by  two  completely 
distinct  elevations  of  secondary  waves,  though  in  the  lowest  part  of 
the  descent  there  may  be  several  minor  inequalities.  The  more  dis- 
tinct of  the  two  occurs  at  about  the  middle  portion  of  the  line  of 
descent.  It  represents  the  dicrotic  wave;  from  its  mode  of  origin  it 
is  sometimes  called  the  "recoil  wave."  Between  the  apex  and  the 
dicrotic  wave  occurs  the  predicrotic,  or  tidal,  wave,  while  below  the 


Fig.  44. — Tracings  Recorded  by  Marey's  Sphygmograph.     (YEO.) 

dicrotic  wave  occurs  the  postdicrotic  wave  (or  waves,  since  there  are 
very  frequently  several). 

The  line  of  ascent  and  the  predicrotic  wave  are  caused  by  systole, 
while  the  dicrotic  wave  takes  place  during  diastole.  The  postdicrotic 
waves  are  a  result  of  vascular  tension. 

Origin  of  the  Dicrotic  Wave. — At  one  time  this  wave  was  be- 
lieved to  have  its  origin  in  the  periphery,  but  is  now  known  to  be 
caused  as  follows:  By  ventricular  systole  there  is  projected  into  the 
full  aorta  a  mass  of  blood  so  that  a  positive  wave  is  propagated  from 
the  heart  toward  the  periphery,  where  it  becomes  extinguished  among 
the  smallest  arterioles  and  capillaries.  At  the  closure  of  the  semi- 
lunar  valves,  the  arteries  from  having  just  been  distended  begin  to 
contract  or  recoil  upon  the  contained  blood,  with  the  result  that  this 
newly  exerted  pressure  sets  it  into  motion  in  two  directions :  toward 
the  heart  and  toward  the  periphery.  In  the  latter  direction  the  pas- 
sage is  free  until  the  capillaries  are  reached;  toward  the  heart  the 
still  closed  semilunar  valves  are  encountered  with  such  force  that 


THE  CIRCULATION.  209 

there  results  a  recoil.    This  develops  into  a  new  positive  wave,  which 
gives  the  dicrotic  wave  in  the  sphygmogram. 

THE  CAPILLARY  CIRCULATION. 

From  anatomy  it  was  learned  that,  with  but  very  few  exceptions, 
blood  passes  into  a  network  of  very  thin-walled  and  hairlike  vessels, 
the  capillaries;  this  network  communicates  with  the  finest  radicles 
of  the  veins,  so  that  it  forms  a  connecting-link  between  the  veins  and 
arteries.  Anatomically,  the  capillaries  are  distinguished  from  the 
arterioles  by  the  absence  of  circularly  arranged  muscular  fibers  which 
the  arterioles  possess  and  by  whose  contraction,  under  vasomotor  influ- 
ence, their  lumina  are  diminished.  However,  the  caliber  of  the  capil- 
laries is  subject  to  change  also  by  reason  of  passive  blood-pressure 
exerted  upon  their  endothelial  cells.  The  real  cause  of  the  blood- 
pressure  in  the  capillaries  is  ventricular  systole;  but  this  is  modified 
by  the  caliber  of  the  arterioles. 

It  is  in  the  interior  of  these  hairlike  vessels  that  fluid  enters  into 
contact  with  organic  tissues  for  their  nourishment  and  growth.  The 
tissues  in  turn  unload  themselves  of  those  effete  and  deleterious  mat- 
ters which  represent  the  products  of  catabolic  processes. 

From  these  reciprocal  actions  between  the  tissues  and  the  blood 
there  result  in  the  latter  profound  modifications  after  it  has  passed 
the  capillary  system.  The  blood  now  presents  the  destructive  charac- 
ters of  venous  blood. 

Placed  between  the  last  ramifications  of  the  arteries  and  the  first 
radicles  of  the  veins,  the  capillary  system  is  blended  with  these  two 
orders  of  vessels  without  the  intervention  of  any  transitional  medium. 
The  limits  assigned  to  this  system  by  anatomy  are  purely  fictitious. 
Physiology  would  be  greatly  embarrassed  if  it  had  to  determine  the 
precise  point  where  the  vessels  are  no  longer  only  organs  of  transport 
for  the  blood,  but  permit  an  exchange  between  the  blood  and  tissues 
through  their  walls.  The  anatomist  places  the  length  of  the  capillary 
at  one-thirtieth  of  an  inch. 

As  previously  stated,  the  capillary  wall  is  formed  entirely  of  a 
simple  layer  of  endothelial  cells.  They  are  flat,  lance-shaped  cells 
joined  edge  to  edge  and  represent  the  continuation  of  the  intima  of  the 
arteries.  The  outlines  of  the  cells  with  their  lines  of  junction  may 
be  beautifully  demonstrated  by  nitrate  of  silver  staining.  In  the 
capillaries  stained  -by  silver  there  is  here  and  there  to  be  seen  between 
the  cells  an  increase  in  the  amount  of  the  intercellular  substance.  The 


210 


PHYSIOLOGY. 


white  blood-corpuscles  when  migrating  from  the  blood-vessels  pass 
between  the  endothelial  cells. 

Microscopical  Examination. — When  a  thin  and  vascular  mem- 
brane belonging  to  a  living  animal  is  placed  in  the  field  of  the  micro- 


Fig.  45.— Frog's  Web,  Highly  Magnified.     (Yso,  after  Huxley.) 

A,  Wall  of  capillary.  B,  Tissue  lying  between  the  capillaries.  C,  Epithe- 
lial cells  of  the  skin.  D,  Nuclei  of  epithelial  cells.  E,  Pigment-cells,  con- 
tracted. F,  Red  blood-corpuscles.  G,  H.  Red  corpuscles  squeezing  their  way 
through  a  narrow  capillary,  showing  their  elasticity.  /,  White  corpuscles. 

scope,  the  admirable  spectacle  observed  for  the  first  time  in  1661  by 
Malpighi  is  seen:  the  Hood  is  circulating  in  the  capillary  vessels. 
For  this  examination  frogs  present  several  parts  which  are  suitable: 
the  interdigital  membrane,  mesentery,  tongue,  bladder,  and  lungs. 


THE  CIRCULATION.  211 

Differences  in  volume  of  the  capillaries  have  much  influence  upon 
the  movement  of  the  blood  in  their  interior.  In  the  widest  capillaries 
a  rapid  current  takes  place,  and  the  corpuscles  are  carried  along  with 
a  velocity  which  does  not  permit  distinguishing  their  form  clearhr.  In 
the  smallest  vessels,  on  the  contrary,  the  corpuscles  progress  slowly. 
In  fact,  the  slowness  of  the  current  and  disappearance  of  the  pulse  are 
the  chief  characteristics  of  the  capillary  current.  For,  normally,  the 
flow  through  the  capillaries  is  in  a  steady,  constant  stream. 

In  the  very  smallest  vessels  the  corpuscles  are  often  at  some  little 
distance  from  one  another.  They  seem  to  advance  with  difficulty  and 
to  rub  against  the  walls  of  the  vessels.  According  to  many  observers, 
the  corpuscles  are  sometimes  obliged  to  bend  out  of  shape  in  order  to 
traverse  these  narrow  channels. 

At  other  times,  in  the  midst  of  the  intricacy  of  the  vessels  and 
of  the  various  directions  of  their  current,  two  capillaries  are  seen  to 
join  a  third.  Corpuscles  coming  along  the  two  vessels  alternately 
pass  into  the  single  capillary,  which  receives  them  one  by  one  and 
through  which  they  pass  in  single  file.  Elsewhere  may  be  seen  a  pile 
of  corpuscles,  distinct  from  each  other,  and  all  of  which  progress  with 
the  same  swiftness.  All  hasten  and  slacken  their  pace  at  the  same 
time.  At  other  points  a  complete  immobility  is  seen  in  consequence 
of  some  temporary  obstruction  or  of  the  contrary  direction  of  the  cur- 
rent; then  all  at  once  the  corpuscles  start  off  again. 

Except  in  the  very  smallest  capillaries,  it  is  noticed  that  the  red 
corpuscles  always  move  in  the  axis  of  the  current,  while  on  either  side 
of  this  thread  of  moving  cells  there  is  noticed  a  transparent  layer  of 
liquor  sanguinis  which  is  almost  perfectly  still  or  possesses  only  slight 
motion.  This  layer,  "  Poiseuille's  still  space,"  where  it  is  plainly 
discernible,  occupies  about  one-fifth  of  the  space  on  each  side  of  the 
axial  current,  which  occupies  three-fifths  of  the  lumen  of  the  vessel. 

Within  the  smaller  blood-vessels  the  red  corpuscles  occupy  the 
middle  of  the  stream,  where,  in  single  file,  they  glide  along  with  com- 
parative rapidity;  in  larger  vessels  two  or  three  may  flow  along 
abreast.  Along  the  outer  edge  of  the  central  thread  of  red  blood- 
corpuscles  move  the  white  ones,  many  even  getting  into  the  space  of 
Poiseuille.  The  motion  of  the  white  corpuscles  is  one  of  rolling,  par- 
ticularly when  they  are  in  the  clear  space  next  the  vessel-wall  or  in 
direct  contact  with  the  latter,  since  they  are  sticky  by  nature.  The 
contact  of  the  rapidly  moving  axis  current  also  assists  in  giving  to  the 
white  corpuscles  their  rolling  motion.  Their  motion  is  so  slow  at 
times  that  they  adhere  to  the  vessel-wall. 


212  PHYSIOLOGY. 

It  has  been  demonstrated  by  physical  experiments  that  particles  of 
least  specific  gravity  (white  corpuscles)  in  all  capillaries  are  pressed 
toward  the  wall,  while  those  of  greater  specific  gravity  (red  corpuscles) 
remain  in  the  middle  of  the  stream. 

One  of  the  characteristics  of  the  capillary  circulation  is  th$  dis- 
appearance  of  the  pulse.  Ordinarily  this  has  been  accomplished  by 
the  resistance  which  is  offered  to  the  current  on  its  way  to  the 
periphery.  When,  for  any  reason,  the  arterioles  are  greatly  relaxed, 
and  there  exists  at  the  same  time  high  blood-pressure,  so  much  blood 
flows  into  the  capillaries  from  the  lessened  resistance  to  its  current  that 
a  distinct  pulse  passes  along  the  capillaries  to  the  veins.  This  pulse 
is  characteristic  of  aortic  insufficiency  or  in  cases  of  atheroma  of  the 
arteries.  In  the  latter  condition  the  vessels  become  calcified  and  rigid 
and  so  behave  physically  as  inelastic  tubes. 

Cause  of  Movement  of  Blood. — The  force  of  the  heart  transformed 
into  arterial  tension  is  the  real  cause  of  the  movement  of  the  blood  in 
the  capillaries.  This  is  not  the  only  influence,  for  gravity  can  exert 
influences  that  are  either  favorable  or  opposed  to  the  current  of  the 
blood. 

Swiftness  of  Blood  in  the  Capillary  System. — Since  very  many 
conditions  are  capable  of  modifying  the  velocity  of  the  blood-current, 
it  is  a  very  difficult  task  to  ascertain  the  numerical  valuation  of  that 
swiftness.  If  the  time  a  corpuscle  takes  to  traverse  a  course  of  a 
known  length  be  measured  under  the  microscope,  a  fairly  accurate 
estimate  can  be  made.  Due  allowances  must  be  made  for  exaggera- 
tions from  the  magnifying  power  of  the  microscope. 

It  is  thus  estimated  that  the  corpuscles  traverse  2  inches  per 
minute  through  the  capillaries  in  man. 

BLOOD=PRESSURE— ARTERIAL  OR  VENOUS  TENSION. 

The  blood-pressure  within  any  vessel  may  be  looked  upon  as  the 
stress  upon  the  inclosed  liquid  at  the  point  of  observation.  Pressure 
of  the  blood  has  been  placed  before  the  student's  attention  quite  fre- 
quently during  the  discussion  of  the  circulation  of  this  vital  fluid.  Its 
consideration  has  been  but  superficial,  however,  up  to  this  point.  The 
blood's  pressure  depends  upon  the  two  factors:  the  peripheral  resist- 
ance and  the  force  of  the  heart.  The  pressure  in  the  circulatory  sys- 
tem varies  with  these  factors  as  variants.  Pressure  will  be  greater 
with  greater  heart-force  or  with  greater  peripheral  resistance.  The 
direction  of  flow  is  always  from  a  point  of  higher  to  one  of  lower 
pressure. 


THE  CIRCULATION.  213 

The  further  the  blood  proceeds  from  that  center  of  circulatory 
motive  power,  the  heart,  the  less  becomes  the  pressure  exerted  by  it. 
It  must  be  greatest,  therefore,  in  the  arteries  emanating  from  the 
heart  and  least  in  those  veins  emptying  into  the  right  heart.  The 
decrease  is  rather  gradual  along  the  vascular  course  until  the  vena} 
cavse  are  reached ;  at  their  point  of  entrance  into  the  heart  the  blood- 
pressure  is  frequently  found  to  be  negative ;  that  is,  below  atmospheric 
pressure. 

Thus,  the  arteries  will  be  found  to  possess  a  pressure  that  is 
peculiar  to  them,  as  do  the  capillaries  and  veins  in  their  turn.  The 


Fig.  40. — Showing  the  Relative  Heights  of  Blood-pressure  in 
Different  Blood-vessels.     (YEO.) 

H,  Heart.  A,  Arteries,  a,  Arterioles.  c,  Capillaries.  V,  Small  veins. 
v,  Large  veins.  H-V,  Being  the  zero-line,  the  pressure  is  indicated  by  the  ele- 
vations of  the  curve.  The  numbers  on  the  left  give  the  pressure  in  milli- 
meters of  mercury. 

intensity  of  the  pressure  will  depend  upon  the  resistances  to  be  over- 
come and  the  vis  a  tergo  that  is  impelling  the  blood-current.  Thus 
the  arterial  pressure  depends  upon  the  relation  existing  between  the 
blood  thrown  out  by  the  ventricles  and  the  quantity  that  can  pass 
through  the  capillaries  in  the  same  time. 

Science  has  possessed  for  a  long  time  the  means  of  knowing  what 
is,  in  inelastic  tubes  which  are  the  seat  of  the  flow,  the  force  of  afflux 
for  each  point  of  their  length,  and  what,  also,  is  the  quantity  of  that 
force  which  has  been  consumed  by  the  resistances  known  as  friction. 


PHYSIOLOGY. 


In  order  that  the  student  may  gain  some  knowledge  of  the  causes 
that  produce  variations  in  the  pressure  as  well  as  the  means  of  meas- 
uring and  recording  it,  attention  will  be  turned  briefly  to  the  physical 
world  to  note  the  simplest  possible  apparatus  that  can  convey  even  a 
vague  idea  of  this  property  of  the  blood's  circulation. 

Suppose  a  reservoir  full  of  liquid  to  a  certain  level,,  and  from  the 
bottom  of  which  runs  a  pipe  of  uniform  caliber.  The  tubes  which 
branch  from  this  main  pipe  are  of  equal  caliber  and  are  placed  at 
equal  distances  from  one  another.  The  upright  tubes  have  received 
the  name  of  manometers.  If,  now,  there  be  a  flow  of  the  liquid  it 
will  be  because  of  a  difference  of  pressure  at  the  reservoir  and  outlet 
due  to  gravitation.  During  this  flow  the  liquid  in  the  various  manom- 
eters will  contain  columns  of  the  liquid  whose  tops  would  be  in  contact 


Fig.  47. — Variations  in  Pressure.     (LANDOIS.) 

A,  Cylindrical  tube  filled  with  water,     a-6,  Outflow  tube,  along  which  are 
placed  at  intervals  the  vertical  tubes,  1,  2,  and  3,  to  estimate  pressure. 

with  a  straight  line  drawn  from  the  superior  surface  of  the  contents 
of  the  reservoir  to  the  point  of  egress.  This  slanting  line  is  known 
as  the  pressure-slope.  The  manometer  nearest  the  reservoir  contains 
the  highest  column  of  liquid,  the  next  one  a  column  of  less  height, 
etc.,  the  lowest  being  attained  in  the  upright  tube  farthest  from  the 
heart  or  reservoir. 

The  height  to  which  the  liquid  rises  in  a  manometer  sensibly  indi- 
cates the  intensity  of  the  force  of  afflux  at  that  point.  And,  as  it 
decreases  from  the  orifice  of  entry  to  that  of  exit,  it  must  be  concluded 
therefrom  that  the  force  of  the  flow  of  the  liquid  decreases  of  itself. 
It  has  been  demonstrated  in  physics  that  the  resistances  which  liquids 
meet  with  in  ducts  of  a  uniform  caliber  are  proportional  to  the  length 
of  the  latter.  It  follows,  therefore,  that,  when  the  flow  is  established 


THE  CIRCULATION.  215 

in  the  tube,  the  more  distant  from  the  ingress  a  point  of  that  tube  is, 
the  more  the  liquid  which  passes  through  it  will  have  lost  its  initial 
force  in  consequence  of  resistances. 

The  more  narrow  the  caliber  of  the  tube,  the  greater  is  the  resist- 
ance to  the  liquid.  Up  to  the  time  of  Eev.  Stephen  Hales,  an  English 
vicar,  the  methods  of  noting  blood-pressure  were  crude  in  the  extreme. 
It  was  known  that  the  blood  exerted  considerable  pressure  upon  the 
arterial  walls,  for,  when  they  were  punctured,  an  intermittent  jet  of 
blood  arose  to  a  considerable  height,  the  latter  depending  upon  the 
proximity  of  the  wound  to  the  heart.  When  a  vein  was  wounded  the 
blood  was  noticed  to  exude  with  much  less  force  and  it  was  continuous, 
not  intermittent. 

Hales  was  the  first  to  make  any  improvement  upon  this  rough 
movement,  which  he  did  by  inserting  a  brass  pipe  one-sixth  of  an  inch 
in  diameter  in  lieu  of  a  cannula  into  the  femoral  artery  of  a  horse 
about  three  inches  from  the  abdomen.  The  brass  pipe  in  the  artery 
was  connected  by  means  of  another  brass  pipe  to  a  glass  tube  whose 
height  was  nine  feet,  its  bore  nearly  the  same  diameter  and  placed 
vertically.  The  first  blood-pressure  experiment  is,  perhaps,  best  de- 
picted in  the  words  of  Hales  himself.  He  says:  "In  December,  1733, 
I  caused  a  mare  to  be  tied  down  alive  on  her  back.  She  was  fourteen 
hands  high,  and  she  had  a  fistula  on  her  withers  and  was  neither  very 
lean  nor  yet  very  lusty.  Having  laid  open  the  left  crural  artery  about 
three  inches  from  her  belly,  I  inserted  into  it  a  brass  pipe  whose  bore 
was* one-sixth  of  an  inch  in  diameter.  To  that,  by  means  of  another 
brass  pipe,  which  was  fitly  adapted  to  it,  I  fixed  a  glass  tube  of  nearly 
the  same  diameter  and  which  was  nine  feet  in  length.  Then,  untying 
the  ligature  on  the  artery,  the  blood  rose  in  the  tube  eight  feet  three 
inches  perpendicular  above  the  level  of  the  left  ventricle  of  the  heart. 
When  the  blood  was  at  its  full  height,  it  would  rise  and  fall  at  and  after 
each  pulse  two,  three,  or  four  inches.  Sometimes  it  would  fall  twelve 
or  fourteen  inches  and  demonstrate  at  that  point  the  same  up-and-down 
vibrations,  at  and  after  each  pulse,  as  it  had  when  it  was  at  its  full 
height.  After  forty  or  fifty  pulses  it  would  rise  to  the  former  height 
again.  Later  I  took  away  the  glass  tube  and  let  the  blood  from  the 
artery  mount  up  into  the  open  air,  when  the  greatest  height  of  its  jet 
was  not  above  two  feet." 

Though  the  first  real  truths  concerning  blood-pressure  were  thus 
gained,  nevertheless  the  method  was  crude  and  cumbersome  in  that  the 
blood  would  soon  clot  and  an  eight-foot  column  of  blood  was  not 
easily  watched  in  its  fluctuations. 


216 


PHYSIOLOGY. 


Poiseuille  in  1828  introduced  into  physiological  experimentation 
a  manometer  with  a  column  of  mercury.  This  instrument  is  more 
convenient  to  handle,  and  with  it  all  of  the  scientific  world  is  ac- 
quainted to-day. 

The  manometer  with  its  column  of  mercury  has  undergone  still 
further  modifications.  Thus,  Magendie  has  employed,  under  the  name 
of  hcemometer,  an  instrument  composed  of  a  mercury  reservoir.  Upon 
this  the  blood-pressure  is  exerted,  and  it  communicates  with  a  tube  in 


Fig.  48. — Manometer  of  Mercury  for  Measuring  and  Regis- 
tering Blood-pressure.     (YEO.) 

a,  Proximal  glass  tube.  &,  Union  of  the  two  glass  tubes  of  the  manom- 
eter, d,  Stop-cock  through  which  the  sodium  carbonate  can  be  introduced 
between  the  blood  and  the  mercury  of  the  manometer,  e,  The  rod  floating  on 
the  mercury  carries  the  writing-point. 

which  the  metal  rises.  The  height  of  the  level  of  the  mercury  in  that 
single  tube  expresses  the  intensity  of  the  pressure. 

By  use  of  the  mercury  as  a  substance  against  which  the  blood  may 
expend  its  force,  the  inconvenience  of  handling  the  great  column  of 
blood  is  overcome. 

One  objection  to  the  mercury  is  that  columns  of  it,  in  their  oscil- 
lations, take  on  acquired  momentum,  which  makes  them  pass  beyond 
the  points  which  exactly  express  the  maximum  and  the  minimum  of 
blood-pressure. 


THE  CIRCULATION. 


217 


When  such  instruments  are  used,  care  must  always  be  taken  to 
prevent  the  coagulation  of  the  blood  by  introducing  an  alkaline  solu- 
tion into  the  points  of  the  apparatus  where  the  blood  must  penetrate. 
The  liquid  most  commonly  used  is  a  saturated  solution  of  sodium 
carbonate. 

In  1847  the  study  of  arterial  tension  entered  a  new  phase,  thanks 
to  the  use  made  by  C.  Ludwig  of  the  apparatuses  with  continuous  indi- 
cations, to  measure  the  variations  which  that  tension  undergoes  under 
the  influence  of  many  conditions.  The  instrument  that  he  used  is 


Fig.  49. — Ludwig's  Kymograph.     (¥EO.) 

R,  Rotating  drum  blackened,  which  is  moved  by  the  clockwork  inclosed 
In  A  by  means  of  the  disc,  D,  pressing  on  the  wheel,  n.  The  cylinder  may  be 
elevated  or  depressed  by  the  screw,  v,  which  is  actuated  by  the  handle,  U. 

known  as  the  kymograph,  or  "wave-writer."  In  brief,  it  consists  of  a 
U-shaped  manometer,  in  the  open  limb  of  which  a  light  float  is  placed 
upon  the  surface  of  the  mercury.  A  writing-style  is  placed  trans- 
versely upon  the  free  end  of  the  float,  which  inscribes  its  movements, 
as  representing  the  oscillations  of  the  mercury,  upon  a  cylinder  which 
revolves  at  a  uniform  rate  by  reason  of  clockwork.  There  is  recorded 
not  only  the  height,  but  its  pulsatile  and  respiratory  oscillations. 

In  looking  at  a  blood-pressure  tracing  we  find  that  the  large 
undulations  are  produced  by  respiratory  movements.  Usually  the 
ascent  is  caused  by  inspiration,  the  descent  by  expiration.  Each  of 
the  small  waves  corresponds  to  heart-action,  the  slight  ascent  to  systole, 


218  PHYSIOLOGY. 

the  slight  descent  to  diastole.  In  studying  a  tracing  it  must  be  re- 
membered that  the  real  blood-pressure  is  really  twice  what  is  recorded, 
since  the  needle  moves  through  a  space  that  represents  the  difference 
of  level  between  the  mercury  of  the  two  tubes. 

Blood=pressure  in  Man. 

Since  it  is  impossible  to  ascertain  blood-pressure  in  man  as  it  is 
practiced  in  animals,,  numerous  instruments  have  been  invented  that 
can  be  used  and  applied  to  superficial  arteries  without  dissection  of 


Fig,  50. — Blood-pressure  Curve  Recorded  by  the  Mercurial  Manom- 
eter.     (YEO.) 

o-x,  Zero-line,  y-y,  Curve  with  large  respiratory  waves  and  small  waves 
of  heart  impulse.  A  scale  is  given  to  show  height  of  pressure  in  millimeters 
of  mercury. 

the  tissues.     These  pieces  of  apparatus  have  been  variously  termed 
spliygmometers,  spJiygmomanometers,  etc. 

The  sphygmomanometer  of  von  Basch  consists  essentially  of  a 
hollow  rubber  pad  or  capsule  containing  liquid  or  air,  and  which  com- 
municates with  a  mercurial  manometer.  The  pad  is  pressed  down 
over  the  artery  till  the  pulse  beyond  it  is  felt  to  disappear  under  the 
finger  or  a  sphygmograph  placed  upon  the  peripheral  portion  of  the 
artery  ceases  to  beat.  The  reading  of  the  manometer  is  then  taken 
as  approximately  equal  to  the  maximum  blood-pressure,  since  the 


THE  CIRCULATION.  219 

tissues  overlying  the  artery  have  been  compressed,  and  therefore 
register  some  pressure. 

Although  numerous  other  instruments  are  upon  the  market,  yet 
the  von  Basch  instrument  is  the  one  most  extensively  used.  It  must 
be  remembered  that  fallacies  exist  in  the  use  of  such  an  instrument. 
For  the  matter  is  only  too  evident  that  there  will  be  recorded  com- 
pression of  the  venae  comites  of  the  artery,  the  skin  and  surrounding 
tissues.  Further,  it  is  impossible  to  tell  the  exact  moment  when  the 
distal  pulse  is  rendered  imperceptible. 

In  the  case  of  healthy,  young  adults,  the  pressure  in  the  brachial 
artery  ranges  between  110  and  130  millimeters  of  mercury.  Pressure 
attains  its  maximum  with  the  individual  in  the  erect  position;  its 
minimum  when  he  assumes  the  horizontal. 

In  unconsciousness  produced  by  chloroform  the  blood-pressure 
falls  about  30  millimeters.  Alcohol  depresses  arterial  tension. 
Faivre,  by  actual  measurement  in  man  during  the  amputation  of  a 
leg,  found  the  mean  pressure  115  millimeters. 

Extremes  of  Pressure. — The  highest  pressure  is  registered  in  the 
aorta.  While  traversing  the  arteries  the  fall  in  pressure  is  very 
gradual.  Immediately  upon  its  passing  from  the  arterioles  into  the 
capillaries  and  there  meeting  great  resistance,  the  pressure  fall  is 
very  marked. 

The  blood-pressure  continues  to  fall  in  the  capillaries  and  veins 
until  the  cardiac  portion  of  the  venaa  cavae  are  reached,  when  the 
lowest  pressure  is  registered.  As  stated  elsewhere,  this  last  pressure 
may  be  negative. 

The  causes  of  alteration  in  blood-pressure  of  arteries,  according 
to  Brunton,  are  as  follows : — 

It  may  be  raised : — 

1.  By  the  heart  beating  more  quickly. 

2.  By  the  heart  beating  more  vigorously  and  more  completely  and 
sending  more  blood  into  the  aorta  at  each  beat. 

3.  By  contraction  of  the  arterioles  retaining  the  blood  in  the 
arterial  system. 

It  may  be  depressed : — 

1.  By  the  heart  beating  more  slowly. 

2.  By  the  heart  beating  less  vigorously  and  completely  and  send- 
ing less  blood  into  the  aorta  at  each  beat. 

3.  By  dilatation  of  the  arterioles,  allowing  the  blood  to  flow,  more 
quickly  into  the  veins. 


220  PHYSIOLOGY. 

4.  By  deficient  supply  of  blood  to  the  left  ventricle,  as  from  con- 
traction of  the  pulmonary  vessels  or  obstruction  to  the  passage  of  blood 
through  them,  or  from  stagnation  of  the  blood  in  the  large  veins,  as 
in  shock. 

The  blood-pressure  in  the  pulmonary  artery  is  about  one-third 
that  of  the  aorta. 

Respiratory  Undulations. — In  studying  a  graphic  record  of  the 
heart's  action  one  is  struck  with  an  almost  rhythmical  rise  and  fall 
of  the  general  tracing.  There  is  thus  depicted  the  condition  of  arterial 
pressure  conjointly  with  the  graphic  representation  of  the  heart-beats. 
They  are  produced  by  the  respiratory  movements,  and  hence  have  been 
termed  respiratory  undulations. 

Cause. — During  inspiration  the  blood-pressure  rises;  during  ex- 
piration it  falls.  Stimulation  of  the  vasomotor  center  is  also  partly 
responsible  for  these  undulations.  This  stimulation  is  produced  by 
the  respiratory  movements  themselves,  which,  by  indirectly  causing 
the  arteries  to  contract,  raise  blood-pressure. 

Traube-Hering  Curves. — These  are  bold  curves  which  are  higher 
than  the  regular  respiratory  undulations,  but  less  frequent.  They  are 
due  to  alterations  in  the  condition  of  the  small  arteries,  superinduced 
by  the  waxing  and  waning  at  regular  intervals  of  the  excitability  of  the 
main  vasomotor  center. 

Vagus  and  Blood-pressure. — When  the  blood-pressure  rises  in  an 
animal  the  usual  sequence  is  for  the  pulse-rate  to  be  diminished  by 
virtue  of  stimulation  to  the  cardio-inhibitory  center  of  the  vagus.  A 
fall  in  the  blood-pressure  is  followed  by  an  increase  in  the  rate  of  heart- 
action.  If  the  pneumogastrics  are  divided  the  pulse  frequency  in- 
creases, and  as  a  result  the  arterial  tension  rises.  If  the  vagi  are 
irritated  the  pulse-rate  falls  and  as  a  sequence  the  arterial  tension 
diminishes. 

If,  however,  the  arterioles  contract,  the  pressure  rises,  and  this 
increase  of  tension  irritates  the  center  of  the  vagus  and  lowers  the 
pulse-rate.  If  the  arterioles  dilate,  the  pressure  falls,  which  lowers 
the  tonus  of  the  vagi,  and  the  pulse  runs  faster.  The  reciprocal 
power  of  the  pulse  and  blood-pressure  to  regulate  each  other  depends 
on  normal  pneumogastrics. 

Pathological. — In  cases  of  granular  or  contracted  kidney,  sclerosis 
of  the  arteries,  and  where  digitalis  is  used  in  heart  affections,  the  blood- 
pressure  is  raised.  Injected  ergotin,  by  causing  contraction  of  the 
arterioles,  also  raises  pressure,  while  morphine  lowers  the  same.  The 
blood-pressure  falls  in  fevers. 


THE  CIRCULATION.  221 

Capillary  Blood-pressure. — Von  Kries  has  estimated  the  blood- 
pressure  in  the  capillaries  of  the  ear  as  about  22  millimeters  of 
mercury. 

Venous  Blood-pressure. — Since  the  pressure  is  so  low  (even  nega- 
tive in  places)  within  this  system,  a  saline  solution  is  usually  sub- 
stituted in  the  manometer  for  mercury.  The  kymographic  tracing 
taken  near  the  heart  shows  the  characteristic  large  and  small  waves, 
with  this  difference,  however,  that  the  respiratory  rise  accompanies 
expiration. 

Venous  pressure  is  increased  by  all  conditions  which  tend  to 
decrease  the  difference  of  pressure  between  the  arterial  system  and 
itself.  The  reverse  will  produce  diminution  in  its  tension.  General 
plethora  increases  it;  anemia  diminishes  it.  There  is  a  mean  nega- 
tive pressure  of  about  —  0.1  millimeter  of  mercury  near  the  heart. 
As  one  proceeds  from  the  heart  there  is  found  the  development  of  a 
positive  pressure. 

In  the  crural  vein  the  blood-pressure  is  about  11  millimeters 
of  mercury. 

RAPIDITY  OF  THE   CIRCULATION. 

When  examining  the  web  of  the  frog's  foot  beneath  the  micro- 
scope it  is  clearly  Discerned  that  the  rate  of  the  blood's  flow  through 
the  capillaries  is  very  much  less  than  what  it  must  be  in  the  aorta  and 
its  larger  branches.  That  there  should  be  differences  in  its  rate 
of  flow  depends  upon  the  same  physical  reasons  as  govern  the  rate  of 
flow  in  tubes,  namely:  resistance,  branching,  size  of  caliber,  and  the 
total  cross-sectional  area. 

If  there  were  no  friction,  the  size  of  the  vessels  would  make  no 
difference.  However,  contact  of  the  fluid  with  the  sides  of  the  vessels 
causes  a  resistance  which  is  proportional  inversely  to  the  diameter  of 
the  vessel :  the  greater  the  diameter,  the  less  the  resistance,  etc. 

The  effect  of  branching  is  to  produce  little  eddies  and  whirls  in 
the  stream,  both  of  which  increase  the  resistance.  In  vessels  of  greater 
caliber  with  the  same  impulsive  power  behind,  the  flow  is  slower  than 
in  those  of  less  caliber. 

Perhaps,  however,  the  one  greatest  factor  influencing  the  rate 
of  flow  is  the  sectional  area  at  any  point.  With  regard  to  it  the  law 
seems  to  be  that  the  velocity  of  the  blood-current  at  any  given  point 
in  the  circulatory  system  is  inversely  proportional. 

The  arterial  system  widens  from  the  center  to  the  periphery. 
All  physiologists  admit  this  proposition,  for  their  opinion  is  founded 


222  PHYSIOLOGY. 

upon  exact  measurements.  It  has  been  found  that,  when  there  is  an 
arterial  bifurcation,  the  area  of  the  two  branches  formed  exceeds 
that  of  the  afferent  trunk.  From  experimental  demonstration  of  the 
widening  of  the  arterial  passages,  the  comparison  of  the  arterial  tree 
to  a  cone  is  permissible ;  its  summit  is  located  at  the  heart,  its  base  at 
the  periphery  of  the  body.  The  venous  system  is  similarly  arranged, 
the  apices  of  the  two  systems  meeting  at  the  heart. 

From  this  general  form  of  the  arterial  passages  it  can  be  con- 
cluded that  the  movement  of  the  blood  must  be  more  rapid  in  the 
aorta  than  in  the  vessels  springing  from  it,  and  that  the  minimum 
of  speed  must  be  in  the  smallest  arterioles.  It  is  known  that  the  cross- 
sectional  area  of  the  arterioles  and  capillaries  is  from  500  to  700 
times  greater  than  that  of  the  first  portion  of  the  aorta;  therefore 
the  velocity  of  the  blood  in  the  capillaries  is  but  1/500  or  1/700  of  that 
in  the  aorta. 

The  resistance  which  the  blood  meets  with  in  the  more  or  less 
shrunken  vessels  is  generally  designated  by  the  misnomer  friction. 
Physics  show  that  there  is  no  real  friction  between  the  walls  of  the 
vessels  and  the  contained  liquid.  The  most  exterior  layer  of  the 
liquid  is  adherent  to  the  inner  surface  of  the  tube  and  remains  per- 
fectly motionless.  The  next  layers  adhere  to  one  another  less  and  less 
the  more  central  they  are.  Thus  the  swiftness  of  the  liquid  molecules 
will  not  be  the  same  in  all  parts  of  the  vessel,  the  maximum  being 
reached  at  the  center  of  the  vessel. 

Bate  in  the  Arteries, — From  the  relation  of  the  arteries  to  the 
main  central  pump,  the  heart,  very  naturally  the  velocity  of  the  blood- 
flow  in  them  is  greater  than  in  the  capillary  or  venous  systems.  In 
rough  terms,  the  average  velocity  in  the  large  arteries  is  12  inches  per 
second.  ;  To  measure  the  velocity  we  employ  Ludwig's  stromuhr,  or 
rheometer.  This  instrument  consists  of  two  glass  bulbs,  1  and  2, 
of  the  same  capacity.  The  ends  of  these  glass  bulbs  have  a  common 
opening  above;  below  they  are  fixed,  at  5-5',  into  a  metal  disc.  This 
disc  rotates  around  the  disc,  6-6',  so  that  after  a  complete  revolution 
a  bulb,  1,  communicates  with  a  cannula,  9,  and  another  bulb,  2,  com- 
municates with  another  cannula,  8.  This  cannula,  8,  is  fixed  in  the 
central  end  and  the  other  cannula,  9,  in  the  peripheral  end  of  the 
artery  (carotid);  the  bulb,  1,  is  filled  with  oil;  the  bulb,  2,  with 
defibrinated  blood.  At  a  certain  time  the  communication  through 
8  is  opened,  the  blood  flows  in,  pushing  the  oil  before  it  and  passes 
into  2,  while  the  blood  passes  through  9  into  the  peripheral  part  of 
the  artery.  As  soon  as  the  oil  reaches  4,  the  time  is  noted,  and  bulbs 


THE  CIRCULATION. 


223 


1  and  2  are  rotated  so  that  2  takes  the  place  of  1,  and  the  oil  is  pushed 
back  into  1  again.  The  quantity  of  the  blood  which  passes  in  a  given 
time  is  calculated  from  the  time  necessary  to  fill  the  bulb. 

Other  instruments  used  have  received  the  names  hcematachometer, 
hcemodromometer,  dromograpli,  etc. 

Kate  in  the  Veins. — Whenever  the  total  area  of  cross-section  of 
the  vascular  tree  increases,  the  velocity  of  its  contained  blood-current 
diminishes;  converse^,  as  the  cross-section  diminishes  the  flow  be- 


Fig.  51. — Luchvig's  Stromuhr.     (LANDOis.) 

comes  proportionately  more  rapid.  The  total  section  of  the  systemic 
arterial  tree  reaches  its  maximum  extent  in  the  arterioles  and  capil- 
laries. Along  the  venous  tree  the  cross-section  diminishes  as  the  heart 
is  neared,  but  never  becomes  as  small  as  that  of  the  arteries.  There- 
fore the  greatest  velocity  must  exist  in  the  arteries,  the  least  within 
the  capillaries,  while  the  mean  between  the  two  extremes  is  that  within 
the  veins. 

Since  the  venous  cross-section  diminishes  as  the  heart  is  neared, 
the   velocity   of   its   blood-current  becomes   heightened    accordingly. 


224:  PHYSIOLOGY. 

However,  the  average  rate  of  venous  blood-flow  has  been  estimated  to 
be  about  9  inches  per  second. 

Rate  in  the  Capillaries. — Even  with  respect  to  the  capillaries  the 
rule  holds  good  that  the  velocity  is  inversely  proportional  to  the  area 
of  cross-section.  In  the  frog  the  velocity  has  been  estimated  to  be 
about  1  inch  per  minute;  among  mammals  it  is  said  to  average  2 
inches  per  minute. 

Marey,  from  a  study  of  the  rapidity  of  the  flow  of  blood,  has 
arrived  at  the  following  conclusions : — 

If  the  resistance  increases  and  the  output  of  the  heart  remains 
constant,  then  the  actual  tension  rises  and  the  velocity  becomes  less. 

If  the  output  of  the  heart  increases  and  the  resistance  remains 
constant,  then  both  the  tension  and  the  velocity  become  greater. 

Ludwig  and  Dogiel  state  that  the  velocity  of  the  blood  does  not 
depend  on  the  mean  blood-pressure.  They  state  the  velocity  in  a  sec- 
tion of  a  vessel  depends  on  (1)  the  vis  a  largo — that  is,  the  action  of 
the  heart;  and  (2)  on  the  peripheral  resistance. 

Duration  of  the  Circulation  as  a  Unit. — The  general  rapidity  of 
the  circulation — that  is,  how  long  a  time  an  entire  circulation  occupies 
— may  be  easily  determined  experimentally  in  a  living  animal.  This 
was  first  accomplished  by  Hering,  whose  principle  of  action  was  to 
compute  the  time  required  for  the  circuit  of  an  injected,  harmless 
substance.  -The  substance  taken  is  one  that  may  be  easily  recognized 
by  chemical  test;  sodium  ferrocyanide  is  the  one  least  injurious  to 
the  heart.  He  injected  a  2-per-cent.  solution  into  the  central  end  of 
a  divided  jugular  vein,  and  the  time  of  injection  was  carefully  noted. 
From  the  opposite  jugular  samples  were  taken  as  quickly  as  possible, 
the  time  of  each  being  noted.  When  the  Prussian  blue  reaction  was 
obtained  in  any  sample,  the  time  of  its  withdrawal  gave  the  duration 
of  the  entire  circuit.  In  this  experiment  the  blood  containing  the 
solution  passed  to  the  right  side  of  the  heart,  through  the  lungs  to 
the  left  side  of  the  heart,  from  thence  into  the  aorta  to  be  distributed 
through  the  smaller  vessels  and  capillaries  of  the  head  and  face,  to 
return  by  the  jugular  veins. 

This  jugular-to- jugular  result  does  not  represent  the  circulation 
of  the  entire  blood-supply  of  the  body,  but  the  shortest  time  that  a 
drop  of  blood  may  traverse  the  shortest  pathway  along  both  the  sys- 
temic and  pulmonic  circulations.  It  is  impossible  thus  to  determine 
the  circulation  time  of  the  entire  blood.  From  the  result  of  experi- 
ments it  has  been  ascertained  that  the  circulation  time  in  the  horse  is 
31.5  seconds;  in  the  dog,  16.7  seconds;  in  the  rabbit,  7.79  seconds. 


THE  CIRCULATION.  225 

Another  method  is  that  of  Prof.  G.  X.  Stewart.  He  injects  into 
a  rabbit  methylene  blue  per  jugular,  and  then,  watching  the  appear- 
ance of  the  coloring  matter  in  the  opposite  carotid,  under  the  carotid 
he  places  a  thin  sheet  of  India  rubber  and  between  this  and  the  artery  a 
little  piece  of  white,  glazed  paper.  Then,  noting  the  time  when  blood 
is  injected  per  jugular  and  the  time  of  its  arrival  in  the  opposite  ca- 
rotid gives  the  duration  of  the  circulation.  In  the  rabbit  he  made  the 
jugular-to-carotid  time  from  5  to  7  seconds. 

In  man  the  time  it  takes  the  blood  to  make  a  complete  circuit  of 
the  body  is  about  32  seconds. 

COURSE  OF  BLOOD  IN  THE  VENOUS  SYSTEM. 

When  the  blood  has  undergone  within  the  general  and  pulmonary 
capillaries  the  changes  which  result  from  processes  of  nutrition  and 
oxidation,  it  returns  to  the  heart.  It  is  the  venous  system  which  is 
charged  with  this  centripetal  transportation. 

Has  the  action  of  the  heart  anything  to  do  with  the  progression 
of  the  venous  blood?  To-day,  all  the  world  recognizes  that  it  is  the 
cardiac  impulsion  which,  after  having  driven  the  blood  through  the 
capillaries,  still  presides.  That  is,  the  venous  blood-current  is  main- 
tained primarily  by  the  vis  a  tergo  (force  from  behind).  In  other 
words,  it  is  what  remains  of  the  systolic  energy  of  the  heart  trans- 
mitted through  the  arteries  and  capillaries.  The  elasticity  of  the 
venous  walls  themselves  aid  to  a  slight  extent  the  movement  of  the 
blood  by  their  rather  feeble  contractions.  Contraction  of  the  skeletal 
muscles,  aspiration  of  the  heart  and  thorax  are  factors  also;  the  last- 
named  condition  creates  the  vis  a  fronte. 

As  the  pulse-wave  is  normally  caused  to  disappear  in  the  capillary 
network,  so  the  blood-pressure  must  suffer  materially  also;  in  fact, 
it  continues  falling  even  along  the  course  of  the  veins  until  the  heart 
is  reached.  Nowhere  along  the  venous  system  is  the  positive  pressure 
more  than  the  merest  fraction  of  what  is  found  along  the  arterial  tree. 
In  the  right  side  of  the  heart  and  the  thoracic  portions  of  the  great 
veins  the  pressure  may  even  be  negative;  that  is,  less  than  the  atmos- 
pheric pressure.  In  the  small  venous  radicles  coming  from  the  capil- 
lary system  the  blood-current  is  more  rapid  than  in  the  capillaries, 
but  much  less  than  the  speed  of  that  attained  in  the  corresponding 
arterioles. 

There  must  of  necessity  be  other  influences  exerted  at  this  stage, 
since  the  energy  which  the  systole  of  the  heart  has  put  forth  has  been 
greatly  expended  before  it  reaches  the  veins. 

15 


226  PHYSIOLOGY. 

At  the  head  of  the  list  of  factors  conducive  to  venous  flow,  other 
than  cardiac  systole,  stands  the  contractions  of  the  skeletal  muscles. 

The  contraction  of  the  muscles  aids  the  passage  of  the  venous 
flow  somewhat  as  follows :  When  pressure  is  brought  to  bear  upon  the 
vein  with  its  contents  at  any  particular  point  naturally  the  contained 
blood  will  endeavor  to  escape  in  two  directions.  That  escaping  toward 
the  capillary  system  is  soon  checked  by  the  closing  of  the  first  pair  of 
valves,  so  that  this  portion  of  the  vein  becomes  swollen  and  distended, 
but  firmly  holds  the  blood.  The  closure  of  the  valves  allows  a  current 
to  be  established  in  but  one  direction,  and  that  toward  the  heart, 
thereby  assisting  venous  flow  in  proportion  to  the  extent  of  pressure 
exerted.  In  the  limbs  is  found  this  aid  to  venous  circulation.  Should 
the  muscles  remain  in  a  state  of  tetanic  contraction,  the  venous  blood 
passing  out  collects  in  the  subcutaneous  system,  for  it  must  be  remem- 
bered that  particularly  numerous  anastomoses  with  one  another,  as 
well  as  the  deep  with  the  superficial  veins,  are  characteristic  of  this 
system.  That  the  muscles  aid  venous  flow  is  nicely  demonstrated  by 
the  increased  flow  from  an  incised  vein  during  contraction  of  its 
adjacent  muscles  when  performing  venesection. 

The  action  of  the  diaphragm  and  intercostals  helps  to  render  the 
intrathoracic  pressure  negative  during  inspiration;  so  that  the  blood 
is  drawn  from  the  peripheral  portion  of  the  venous  tree  toward  the 
heart;  as  some  observer  states  it,  the  blood-column  is  actually  lifted 
in  the  ascending  vena  cava. 

Another,  though  less  important,  factor  in  venous  propulsion  is 
thoracic  suction.  For  every  time  that  the  chest  expands  and  makes 
in  its  interior  an  empty  space,  air  rushes  in  to  fill  the  same.  The 
venous  blood,  situated  in  the  vicinity  of  that  cavity,  also  is  helped 
into  its  intrathoracic  veins. 

CIRCULATION  IN  THE  BRAIN. 

Dr.  Leonard  Hill  states  that  the  brain  content  of  blood  can  vary 
suddenly  only  to  a  slight  degree,  and  that  Monro's  doctrine  is  to  all 
intents  and  purposes  true.  When  the  aortic  pressure  rises  the  expan- 
sion of  the  cerebral  volume  can  take  place  only  to  a  certain  limited 
amount,  for,  as  soon  as  all  the  cerebro-spinal  fluid  is  driven  out  from 
the  cranium,  the  brain  everywhere  is  in  contact  with  the  rigid  skull. 
We  have  in  the  vasomotor  center  a  protective  mechanism  by  which 
blood  can  be  drawn  at  need  from  the  abdomen  and  supplied  to  the 
brain.  At  the  moment  of  excitation  from  the  external  world  the 
splanchnic  area  contracts  and  more  blood  is  driven  through  the  brain. 


THE  CIRCULATION.  227 

The  quantity  of  blood  in  the  brain  is  the  same,  but  the  rapidity  of 
circulation  in  the  brain  varies.  Thus,  should  there  be  any  evidence  of 
cerebral  congestion,  the  splanchnic  fibers  dilate  the  vessels  in  its  area, 
and  by  so  doing  decrease  the  amount  sent  to  the  cavity  of  the  cranium. 
Should  cerebral  anaemia  occur,  the  reverse  will  be  the  condition  of 
affairs  in  the  splanchnic  area. 

VASOMOTOR  NERVOUS  SYSTEM. 

Thus  far  the  circulatory  system,  except  the  heart,  has  been  con- 
sidered almost  entirely  from  its  physical  standpoint:  that  it  is  a 
system  of  more  or  less  elastic  tubes  through  which  the  blood  is  pro- 
pelled by  the  action  of  the  heart.  There  was  considered  the  resistance 
which  its  passage  met  with,  the  pressure  exerted  by  this  vital  fluid, 
with  the  interpretations  and  the  physical  causes  for  variations  in  each 
function  or  property.  It  yet  remains  to  consider  that  they  are  living 
tubes,  and  that  they  and  the  heart  are  kept  in  a  very  delicate  balance 
by  reason  of  certain  physiological  mechanisms.  The  agents  governing 
their  functions  are  impulses  that  emanate  from  the  central  nervous 
•system  via  certain  nerves.  The  circulatory  apparatus,  as  every  other 
system,  organs,  or  parts  of  the  entire  economy,  is  under  one  manage- 
ment and  direction  located  within  the  central  nervous  system.  It  is 
this  latter  system,  by  the  maintenance  of  its  functions,  that  produces 
harmony  and  division  of  labor  throughout  the  entire  body. 

It  has  been  previously  stated  that  the  musculature  of  the  heart 
is  under  the  guidance  of  two  sets  of  nerve-fibers :  one  set  to  restrain 
heart-action;  another  to  increase  it.  Likewise  there  are  two  sets  of 
fibers  which  supply  the  musculature  of  the  vessels  (particularly  the 
.arterioles,  since  their  proportionate  quantity  of  circular,  unstriped 
muscular  fibers  is  greatest),  which,  together  with  their  centers,  con- 
stitute the  vasomotor  system. 

The  vasomotor  system  may  be  said,  then,  to  be  composed  of  the 
vasomotor  center,  situated  in  the  medulla,  together  with  some  accessory 
and  subsidiary  centers  in  the  spinal  cord,  and  vasomotor  nerves.  The 
nerves  are  divided  into  two  classes,  according  as  they  increase  or 
diminish  the  caliber  of  the  arterioles:  those  which  increase  the  caliber 
are  vasodilators;  those  which  diminish  the  same  are  known  as  vaso- 
constrictors. All  nerves  that  in  any  way  influence  vessel-caliber  are 
classed  under  the  general  head  of  vasomotor. 

How  the  Nerves  End. — The  manner  in  which  the  nerves  end  in 
the  walls  of  the  blood-vessels  is  an  important  subject.  According  to 
the  majority,  the  arrangement  is  as  follows:  First  there  is  a  funda- 


228  PHYSIOLOGY. 

mental  plexus  whose  fibers  are  interwined  upon  the  external  coat  of 
the  blood-vessel.  These  fibers  are  both  gray  and  white.  Then  there 
is  a  second  plexus  located  in  the  structure  of  the  external  coat  of  the 
artery  and  which  is  made  up  of  fibers  from  the  first,  or  fundamental, 
plexus.  When  the  fibers  of  this  plexus  enter  the  external  coat  of  the 
artery,  they  lose  their  neurilemma,  and  at  the  same  time  they  present 
numerous  nodules  on  their  tract.  Then  follows  the  third  plexus :  the 
intramuscular  one.  It  is  composed  of  very  fine  filaments  arising  from 
the  second  plexus,  terminating  in  the  muscular  fibers. 

Though  the  capillaries  are  known  to  have  nerve-fibers  surrounding 
them,  yet  there  has  not,  as  yet,  been  demonstrated  any  change  in  their 
lumen  as  a  result  of  direct  stimulation  to  these  same  nerve-fibers. 
With  the  exception  of  the  portal  system,  there  has  not  been  established 
any  direct  proof  of  function  of  vasomotor  nerves  in  regard  to  the 
venous  system. 

Stilling  in  1840  knew  that  the  vascular  nerves  ran  in  the  sympa- 
thetic, and  he  named  these  nerves  vasomotors.  Claude  Bernard  in 
1851  found  that  after  section  of  the  cervical  sympathetic  the  blood- 
vessels of  the  ear  dilated  and  the  ear  became  warmer.  In  1852 
Brown-Sequard  discovered  that  electrical  irritation  of  the  cranial  end 
of  the  sympathetic  was  followed  by  a  contraction  of  the  blood-vessels 
and  that  this  contraction  was  succeeded  by  a  lowering  of  the  tem- 
perature of  the  ear. 

In  1858  Bernard  found  that  when  the  chorda  tympani  was  irri- 
tated the  blood-vessels,  instead  of  being  constricted,  are  dilated.  To 
such  an  extent  does  dilatation  occur  that  the  blood  in  the  vein  acquired, 
instead  of  a  blue  color,  a  red  color.  The  veins  themselves  became 
swollen  in  size. 

These  various  observations  tend  to  prove  that  there  are  two  kinds 
of  vasomotor  nerves :  vasoconstrictors  and  vasodilators. 

Functions. — Ordinarily  the  arterioles  are  in  a  state  of  tonicity— 
moderate  contraction — to  maintain  peripheral  resistance;  otherwise 
the  flow  of  blood  through  the  capillaries  would  be  intermittent  instead 
of  continuous,  as  it  normally  is.  It  is  when  this  peripheral  resistance 
is  low  that  there  appears  a  capillary  and  venous  pulse. 

In  hot  weather  the  capillaries  of  the  skin  dilate ;  in  cold  weather 
they  contract. 

Another  very  important  function  of  the  vasomotors  is  their  regu- 
lation of  the  amount  of  blood-supply  to  any  part,  organ,  or  gland  of 
the  economy.  That  is,  they  govern  the  amount  found  within  the 
arterioles  and  capillaries  of  the  tissues. 


THE  CIRCULATION.  229 

The  vasoconstrictor  nerves  arise  from  a  center  in  the  medulla 
oblongata,  pass  down  the  lateral  columns,  and  establish  communication 
with  minor  vasomotor  centers  in  the  spinal  cord,  and  then  the  vaso- 
motor  fibers  from  there  emerge  by  the  anterior  roots  to  reach  the  blood- 
vessels. 

When  a  vasoconstrictor  nerve,  as  the  sympathetic,  is  cut,  the 
blood-vessels  of  the  rabbit's  ear  supplied  by  it  dilate.  This  fact  indi- 
cates that  the  circulatory  vessels  have  tonic  impulses  going  to  them 
from  the  central  nervous  system  through  the  vasoconstrictor  nerves. 

This  tonus  of  the  vasoconstrictor  nerves  does  not  exist  in  all  vaso- 
motor nerves  to  the  same  degree.  It  is  a  variable  factor — may  be 
depressed  or  absolutely  removed.  To  decide  that  a  nerve  is  a  vaso- 
constrictor nerve,  it  becomes  necessary  to  irritate  the  nerve  with  an 
electrical  current  and  then  to  see  the  blood-vessels  supplied  by  it 
contract. 

When  tonus  exists  in  a  vasoconstrictor  nerve  and  it  is  then  cut, 
there  results  an  effect  opposite  to  that  of  an  irritation.  That  is,  there 
is  a  condition  of  dilatation  in  the  arterioles  and  capillaries.  By  this 
section  of  the  vasoconstrictors  the  volume  of  the  parts  increases  in 
direct  proportion  to  the  increased  blood-supply.  If  a  cut  be  made 
into  the  organ,  the  blood  flows  more  rapidly  than  before  there  was 
section  of  the  nerve.  The  temperature  of  the  organ  increases  and  is 
perceptibly  higher  than  that  of  the  opposite  side. 

With  increase  in  dilatation  there  is  a  concomitant  fall  in  blood- 
pressure.  If  a  large  vasoconstrictor  nerve  like  the  splanchnic  be  cut, 
then  the  blood-pressure  is  marked  by  a  most  decided  fall. 

If,  now,  the  vasoconstrictor  be  irritated,  preferably  with  elec- 
tricity, phenomena  that  are  opposite  to  those  just  detailed  ensue.  The 
arterioles  and  capillaries  become  so  contracted  that  they  are  no  longer 
visible ;  the  size  of  the  organ  supplied  by  these  nerves  diminishes ;  the 
venous  blood  becomes  dark.  If  you  cut  the  organ,  less  blood  flows 
out  of  it  than  when  there  is  paralysis  of  the  constrictors  and,  there- 
fore, dilatation. 

The  vasomotor  nerves  are  always  in  a  condition  of  antagonism, 
although  the  constrictor  influence  is  by  far  the  more  powerful.  Thus, 
if  a  nerve-trunk  which  contains  both  constrictor  and  dilator  fibers  bfe 
stimulated,  the  first  effect  is  constriction  of  the  arterioles  and  capil- 
laries supplied  by  the  artery.  This  condition  of  constriction  lasts  for 
some  time,  but  is  eventually  replaced  by  dilatation  of  the  vessels  of  the 
part.  This  dilatation  is  a  sequel,  and  is  to  be  explained  by  the  fact 
that  the  vasodilator  fibers  are  less  easily  exhausted  than  are  the  vaso- 


230  PHYSIOLOGY. 

constrictor  fibers.  For,  after  separation  of  the  vasomotor  fibers  from 
the  central  nervous  system,,  it  is  found  that  the  vasodilator  fibers  do  not 
lose  their  excitability  before  the  lapse  of  from  six  to  ten  days.  The 
vasoconstrictor  fibers  do  not  respond  to  excitation  after  the  third  or 
fourth  day. 

Vasoconstrictors  of  the  Head. — It  is  known  that  the  cervical 
sympathetic  is  the  vasoconstrictor  for  the  corresponding  side  of  the 
face,  ear,  cheeks,  lips,  brow  and  iris,  middle  ear,  tongue,  with  the 
submaxillary  and  parotid  glands ;  in  fact,  all  parts  of  the  head  with 
the  exception  of  the  brain  are  supplied  by  it  with  its  corresponding 
sympathetic.  Now,  these  vasoconstrictors  do  not  arise  from  the  sym- 
pathetic ganglia,  but  spring  from  the  spinal  cord  by  means  of  their 
rami  communicantes.  The  fibers  that  are  destined  for  the  supply  of 
the  head  and  neck  proceed  to  the  first  thoracic  ganglion,  thence  along 
the  annulus  of  Vieussens  to  the  inferior  cervical  ganglion  to  the  sym- 
pathetic trunk,  along  which  and  its  branches  they  reach  their  respec- 
tive destinations. 

Vasoconstrictors  of  the  Extremities. — The  fibers  that  are  in- 
tended for  the  supply  of  the  body-wall  and  limbs  pass  back  by  the 
gray  rami  communicantes  to  be  distributed  to  these  parts  with  the 
other  spinal  nerve-fibers. 

The  origin  of  the  constrictors  of  the  anterior  extremities  is 
probably  from  the  middle  part  of  the  dorsal  segment  of  the  spinal 
cord.  As  to  the  peripheral  course  of  these  nerves,  a  part  of  them  run 
with  the  nerves  of  the  arm  and  from  these  to  the  blood-vessels,  while 
a  part  run  directly  from  the  sympathetic  in  the  plexuses  to  spin  around 
the  blood-vessels  and  their  branches.  The  vasoconstrictors  of  the  pos- 
terior extremities  have  given  more  definite  results,  and  are  found  to 
spring  from  the  cord  in  conjunction  with  the  eleventh,  twelfth,  and 
thirteenth  dorsal  nerves  of  animals,  as  well  as  the  first  and  second 
lumbar  nerves  of  animals.  The  constrictors  unite  with  the  large 
nerve-trunks  and  with  their  branches  go  to  the  extremities. 

Vasoconstrictors  of  the  Abdominal  Viscera. — The  fibers  for  the 
interior  of  the  economy  pass  into  the  various  plexuses  of  the  sympa- 
thetic nerves  in  the  thorax,  abdomen,  and  pelvis,  to  be  distributed  to 
the  vessel-walls  of  the  various  viscera  contained  within  these  several 
cavities.  The  grouping  includes  the  most  important  vasomotor  nerves 
of  the  body,  the  splanclinics. 

If  one  splanchnic  be  cut  in  the  abdominal  cavity,  the  blood- 
pressure  sinks  30  or  40  millimeters;  if  the  second  be  cut  the  pressure 
immediately  drops  to  10.  If  the  peripheral  end  of  the  cut  nerve  be 


THE  CIRCULATION.  231 

irritated,  the  aortic  pressure  ascends  and  reaches  as  great  a  height  as 
it  had  before  section.  Through  the  paralysis  of  the  abdominal  vessels 
the  portal  system  is  filled  with  blood,  the  small  intestinal  vessels  are 
strongly  injected,  the  blood-vessels  of  the  kidneys  are  dilated,  and  the 
renal  tissue  is  red  and  congested. 

By  these  experiments  it  was  established  that  the  splanchnic  is  the 
most  important  of  all  the  vasoconstrictor  nerves,  and  therefore  an 
important  regulator  of  the  blood-pressure.  The  constrictors  of  the 
splanchnics  all  arise  from  the  tenth  dorsal  to  the  fifth  dorsal  ganglia. 
The  splanchnics  supply  vasomotor  fibers  to  the  stomach,  bowels,  and 
kidneys.  Irritation  of  one  splanchnic  is  sufficient  to  cause  vasocon- 
striction  in  both  kidneys. 

The  viscera  receive  vasoconstrictor  fibers  from  other  sources,  as 
the  vagus.  The  peripheral  vasomotor  ganglia  localized  in  the  walls 
of  the  blood-vessels  also  help  to  exert  a  sort  of  tonus  over  the  caliber 
of  the  vessels.  This  statement  is  based  upon  the  fact  that,  two  weeks 
after  performing  section  of  both  splanchnics  beneath  the  diaphragm, 
the  blood-pressure  is  again  found  to  be  the  same  as  that  of  a  normal 
animal. 

Vasoconstrictors  of  the  Lungs.— When  the  central  end  of  the 
splanchnic  is  irritated  the  blood-pressure  rises  in  the  arteries  of  the 
lungs,  since  a  greater  amount  of  blood  is  driven  into  the  inferior  vena 
cava.  Similarly,  an  obstructive  lesion  of  the  left  heart  will  elevate 
blood-pressure  in  the  lungs.  But  direct  observation  shows  that  the 
vasoconstrictors  of  the  lungs  are  not  strongly  developed. 

Vasodilators. — The  vasodilators  originate  from  a  principal  center, 
located  in  the  medulla  oblongata,  and  from  subsidiary  centers  dis- 
tributed throughout  the  spinal  cord.  As  a  rule,  these  nerves  are 
mingled  with  the  vasoconstrictors ;  but  there  are  exceptions.  Their 
inclination  is  to  emerge  through  the  cerebro-spinal  nerves,  while  the 
constrictors  are  generally  mixed  with  the  great  sympathetic  system. 
Their  region  of  egress  is  not  so  limited  as  that  of  the  vasoconstrictors, 
since  the  nervi  erigentes  originate  as  low  down  as  the  second  and  third 
sacral  nerves,  while  the  chorda  tympani  is  a  branch  of  the  seventh 
cranial  nerve.  The  chorda  tympani  and  the  nervus  erigens  are  pure 
vasodilator  nerves :  that  is,  they  contain  no  vasoconstrictors. 

While  the  vasodilators  usually  emerge  through  the  cerebro-spinal 
nerves,  the  student  must  remember  that  the  distributions  of  the  two 
nerves  are  far  different. 

All  vasomotor  nerves  are  distributed  to  unstriped,  involuntary 
muscles;  spinal  nerves  to  striped  voluntary  muscles.  The  former  are 


232  PHYSIOLOGY. 

always  characterized  by  being  ganglionated ;  in  other  words,  possess- 
ing cell-stations,  or  relays,  in  their  course  from  the  central  nervous 
system  to  the  muscular  fibers  which  they  govern. 

The  vasodilator  nerves  behave  very  similarly  to  the  cardiac 
branches  of  the  vagus,  for,  when  both  are  stimulated,  the  result  pro- 
duced is  inhibition  and  relaxation.  Vasodilation  results  from  direct 
stimulation  of  the  center  in  the  medulla.  Thus,  during  asphyxia  the 
strongly  venous  blood,  while  it  stimulates  the  vasoconstrictor  center 
so  as  to  diminish  the  caliber  of  the  splanchnic  area,  also  stimulates  the 
dilator  center  to  produce  relaxation  of  the  cutaneous  vessels.  Nicotine 
is  said  to  be  a  powerful  excitant  of  the  vasodilators. 

Recognition. — It  is  easy  to  recognize  a  vasodilator  nerve  when 
it  contains  no  other  fibers.  But,  should  it  be  mixed  with  vasocon- 
strictors going  to  the  same  organ,  it  becomes  necessary  to  make  special 
arrangements.  These  are  occasioned  from  the  fact  that  the  vaso- 
constrictors usually  overcome  the  dilators.  However,  the  constrictors 
become  tired  more  quickly,  and  after  they  are  exhausted  the  vaso- 
dilators act. 

By  warming  or  cooling  an  extremity  with  water,  the  experimenter 
can,  on  irritating  a  nerve,  obtain  a  dilatation  or  a  narrowing  of  the 
blood-vessels  supplied  by  it.  When  in  the  same  nerve  two  kinds  of 
vasomotors  run,  then  by  the  same  irritation  in  warming  the  foot  there 
is  obtained  a  contraction  of  the  vessels,  and  in  the  second  place  a 
dilatation  on  cooling  the  foot. 

Differences  in  Two  Kinds  of  Nerves. — Vasomotor  nerves  present 
differences  in  their  actions  dependent  upon  division  and  degeneration 
in  the  same.  After  degeneration,  an  irritant  to  a  nerve  calls  out  vaso- 
dilation,  while  to  a  nerve  in  the  fresh  state  the  same  irritant  produces 
a  primary  vasoconstriction. 

By  variation  in  the  frequency  and  strength  of  the  irritation  there 
is  afforded  a  means  to  differentiate  the  two  kinds  of  nerves  \vhich  may 
traverse  the  same  nerve-trunk.  The  vasodilators  are  excited  by  weak. 
currents  and  slow  rhythm.  The  vasoconstrictors  are  irritated  by 
stronger  currents  and  greater  frequency  of  irritation. 

Path  of  Vasodilator  Nerves. — The  dilators  of  the  submaxillary 
glands  and  tongue  come  from  the  facial  to  pass  along  the  chorda 
tympani  to  the  gland.  To  reach  the  anterior  two-thirds  of  the  tongue 
the  vasodilators  traverse  the  lingual ;  to  supply  the  posterior  third  the 
course  is  along  the  glosso-pharyngeal. 

The  mucous  membrane  of  the  cheek,  lips,  and  gums,  as  well  as  the 
nasal  openings,  receive  their  vasodilators  from  the  trigeminus. 


"  THE  CIRCULATION.  233 

The  vasodilators  of  the  anterior  extremities  arise  from  the  fifth 
and  eighth  dorsal  nerves.  The  posterior  extremities  receive  their  sup- 
ply of  vasodilators  from  the  second  to  third  lumbar  nerves. 

The  splanchnic  nerves  also  contain  vasodilator  fibers.  Thus  the 
cervical  sympathetic  and  splanchnics,  which  have  always  been  regarded 
as  great  vasoconstrictors,  are  also  rich  in  vasodilators. 

Muscles  are  supplied  only  with  vasodilator  nerves. 

Theory  of  Vasodilator  Action. — The  vasodilators  must  act  upon 
the  circular  arterial  muscle,  either  directly  or  indirectly.  How  they 
act  is  still  hypothetical.  Since  physiologists  know  of  no  muscle 
through  whose  contraction  the  blood-vessels  become  more  dilated,  it 
is  assumed  that  vasodilation  is  due  to  a  paralysis  of  the  circular  fibers 
of  the  vessels.  That  is,  the  dilators  must  be  inhibitory  or  vaso-inhib- 
itory  nerves. 

The  tonus  of  a  blood-vessel  depends  partly  upon  impulses  from 
the  central  nervous  system  via  the  vasoconstrictors  and  partly  from 
the  influence  of  centers  lying  in  the  vicinity  of  the  vessel.  It  is  upon 
these  latter  centers  that  the  dilators  are  supposed  to  exert  an  inhibitory 
action;  so  that  the  centers  lose  their  influence  upon  the  vessel,  which 
promptly  proceeds  to  dilate  ,to  its  greatest  extent. 

As  support  of  the  existence  of  these  peripheral  vasomotor  centers 
the  following  has  been  noted :  After  section  of  the  vasoconstrictors  and 
without  their  reunion,  after  the  lapse  of  a  few  weeks  tonus  is  again 
attained.  This  end  is  accomplished  by  reason  of  the  peripheral  centers 
keeping  the  muscles  of  the  blood-vessels  contracted. 

Frequent  allusions,  during  the  discussion  of  the  vasomotor  system, 
have  been  made  to  the  effects  of  experiments  upon  various  vasomotor 
nerves.  They  have  been  nearly  all  performed  upon  animals,  and  con- 
sist, in  the  main,  of  section  and  excitation  of  various  kinds :  electrical, 
thermal,  etc.  By  these  means  much  has  been  learned  concerning  this 
very  important  system — important  to  the  physician  as  a  means  of  ex- 
plaining many  pathological  conditions. 

Vasomotor  Centers. — The  main  vasomotor  center  lies  in  the  floor 
of  the  fourth  ventricle  in  its  gray  matter.  It  is  located  on  each  side  of 
the  median  raphe,  to  extend  three  millimeters  from  a  little  above 
the  nib  of  the  calamus  scriptorius  to  near  the  corpora  quadrigemina. 
Its  position  was  determined  by  noting  that  when  it  was  destroyed 
there  was  a  lack  of  tonicity  displayed  by  all  of  the  arterioles,  with 
a  consequent  fall  in  blood-pressure.  When  this  same  area  was  stimu- 
lated all  of  the  arterioles  were  constricted,  giving  a  rise  in  blood- 
pressure  as  a  sequel.  Section  of  the  cervical  spinal  cord  permits  all 


234  PHYSIOLOGY. 

the  arterioles  to  dilate,  as  the  main  vasomotor  center  has  been  cut  off, 
and  the  blood-pressure  falls  to  10  millimeters. 

SPINAL  VASOMOTOR  CENTERS. — Experiments  demonstrate  that 
with  the  destruction  or  paralysis  of  the  main  center  there  results  a 
drop  in  blood-pressure;  if,  however,  the  animal  be  kept  alive  by  arti- 
ficial respiration,  after  a  variable  length  of  time  the  arterioles  regain 
their  tonicity  and  there  is  a  corresponding  rise  in  pressure.  This 
phenomenon  is  accounted  for  by  the  presence  of  minor  or  subsidiary 
centers,  which  in  the  emergency  have  risen  in  their  functional  abili- 
ties. These  minor  vasoconstrictor  centers  exist  in  the  spinal  cord. 
They  may  be  excited  in  a  reflex  manner  by  means  of  strychnine  (Ott 
and  Klapp). 

Upon  destruction  of  the  cord  there  follows  a  second  fall  of  pres- 
sure, with  dilatation  of  the  arterioles.  The  spinal  vasoconstrictor 
centers  exist  in  the  upper,  dorsal  part  of  the  spinal  cord.  As  to  the 
peripheral  vasomotor  centers,  they  exist  in  the  blood-vessels;  those  in 
the  rabbit's  ear  cause  rhythmical  movements  from  two  to  eight  times 
per  minute. 

The  vasoconstrictor  center  is  in  a  state  of  permanent  excitation, 
which  produces  vascular  tonus;  this  is  not  the  case  with  the  vaso- 
dilator center. 

In  a  totally  relaxed  vascular  system  there  is  no  possible  circula- 
tion— the  blood  stands  still.  During  extreme  dilatation  the  heart  re- 
ceives but  little  blood,  so  that  but  very  little  is  driven  out  of  it  during 
systole.  Hence  the  tonus  of  the  blood-vessels  is  a  necessary  condition 
for  the  circulation. 

The  tonus  of  the  veins  is  dependent  upon  the  central  nervous 
system,  and  its  tonus  is  quite  as  important  as  is  that  for  the  arteries. 

The  vascular  tonus  is  continually  a  seat  of  slight  fluctuations,  of 
which  the  most  important  when  depicted  graphically  constitute  the 
curves  of  Traube.  The  curves  are  the  products  of  oscillations  of  the 
vascular  tonus.  The  oscillations  are  caused  by  variations  in  the  auto- 
matic excitation  of  the  vasoconstrictor  centers.  '  ( See  "  Traube-Hering 
Curves.") 

The  vasoconstrictor  center  is  excited  during  dyspnoea  and  as- 
phyxia. This  occurs  on  account  of  the  accumulation  of  carbonic  acid 
in  the  blood.  This  action  explains  why  the  arteries  in  the  cadaver  are 
free  from  blood.  Strychnine,  nicotine,  and  Calabar  bean  also  excite 
the  vasoconstrictor  center. 

Advantages  of  Vessel  Innervation. — By  reason  of  vascular  tonic- 
ity the  diameters  of  the  vessels  are  a  trifle  too  small  to  contain  all  the 


THE  CIRCULATION.  235 

blood;  so  that  the  vascular  walls  are  obliged  to  dilate.  The  result 
is  pressure  and  circulation  of  the  blood. 

When  various  organs  and  parts  of  the  body  are  in  activity  they 
require  an  excess  of  blood.  This  surplus  is  furnished  by  a  dilatation 
of  the  capillaries  of  the  part.  Ludwig  compared  the  vasomotor  centers 
to  turn-cocks  in  a  great  city.  They  turn  off  the  water-supply  from  one 
district  and  at  the  same  time  turn  it  on  in  another. 

As  previously  stated,  the  cutaneous  circulation  regulates  the  losses 
of  heat. 

When,  from  the  influence  of  cold,  the  capillaries  of  the  skin  are 
narrowed,  the  internal  organs  are  congested.  Under  the  action  of  heat 
the  skin  is  congested  and  the  internal  organs  made  anaemic.  This 
increase  in  the  blood-supply  in  those  parts  where  needed  has  been 
ingeniously  demonstrated  by  Mosso.  He  placed  a  man  upon  a  very 
large  board  which  was  most  delicately  balanced  at  its  center.  By  use 
of  it  he  demonstrated  that  whenever  the  man  began  to  think  the  in- 
creased blood-supply  in  his  brain  caused  the  head  to  go  down  and  the 
heels  to  rise  up. 

Vasomotor  Center  Reflexly  Excited. — Like  the  cardiac  nerves,  so 
the  vasomotor  nerves  of  all  parts  of  the  body  may  be  excited  reflexly. 

We  have  reflex  action  in  making  lines  upon  our  skin  with  a  blunt 
instrument,  in  the  warming  of  the  skin,  in  the  vascular  injection  upon 
opening  of  the  abdominal  cavity,  and  in  the  vascular  dilatation  of  the 
vessels  of  the  pia  mater  of  the  brain  when  the  skull  cavity  is  opened. 

By  irritation  of  the  mucous  membrane  of  the  nose  there  is  seen  a 
vascular  disturbance  of  the  whole  head.  If  one  hand  be  plunged  into 
ice-water,  the  blood-vessels  of  the  opposite  hand  also  contract.  Thus, 
irritation  of  any  sensory  nerve  in  the  body  causes,  as  a  rule,  a  contrac- 
tion of  the  blood-vessels  and  especially  those  supplied  by  the  splanch- 
nics.  The  blood-vessels  of  the  skeletal  muscles,  as  a  rule,  dilate  after 
irritation.  With  the  single  exception  of  the  nervus  depressor,  irrita- 
tion of  any  sensory  nerve  is  followed  by  a  rise  of  blood-pressure.  The 
rise  which  is  created  depends  upon  the  strength  and  nature  of  the 
stimulus.  During  this  condition  there  is  vasoconstriction  of  the 
splanchnic  vessels,  while  at  the  same  time  the  blood-vessels  of  the  skin 
and  muscles  are  more  or  less  dilated.  The  reflexes  that  depress  the 
arterial  tension  are  due  to  the  nervus  depressor.  This  condition  of 
depression  is  due  to  a  vasodilation  of  the  arterioles,  especially  in  the 
vessels  supplied  by  the  splanchnics. 

The  vasomotor  changes  can  be  studied  by  means  of  instruments 
which  register  the  changing  volume  of  a  part  at  each  systole  of  the 


236  PHYSIOLOGY. 

heart  and  the  varying  diameter  of  the  arterioles.  These  instruments 
are  known  by  the  names  of  plethysmo graph  and  oncometer. 

Pathological  Conditions  of  Vasomotor  Action.  — Hemicrania  is 
due  to  unilateral  contraction  of  the  carotid  branches  going  to  the  brain. 
In  exophthalmic  goiter  the  vasomotor  system  is  implicated. 

The  secretion  of  the  urine  is  to  a  great  extent  under  the  varying 
tension  due  to  vasomotor  activity.  In  fever  the  vasomotor  system  is 
concerned  in  the  flushing  of  the  face  and  body. 


CHAPTER  VII. 

RESPIRATION. 

THE  study  of  digestion  and  circulation  has  taught  the  reader  the 
nature  of  the  methods  and  the  avenues  along  which  ingested  materials 
must  pass  in  the  processes  of  their  elaboration  in  order  to  maintain  the 
requirements  of  life.  It  has  also  made  him  acquainted  with  the 
various  forms  under  which  those  materials  became  absorbable  and 
miscible  with  the  blood,  and  which  must  necessarily  be  renewed  in 
proportion  as  the  latter  is  changed  by  the  nutrient  movement.  It  is 
known,  too,  that  the  liquid  and  soluble  products  of  digestion  and  the 
lymph  itself,  when  poured  into  the  venous  blood,  do  not  have  the  qual- 
ities of  a  directly  nutrient  fluid  immediately  after  their  mixture  with 
the  blood.  In  order  that  these  qualities  should  develop  it  is  necessary 
that  there  occur  the  intervention  of  an  essential  element,  which  ani- 
mals find  in,  and  incessantty  draw  from,  the  enveloping  atmosphere — 
oxygen.  The  latter  is  the  great  agent  in  the  final  transformations 
which  the  various  organic  matters  must  undergo.  The  introduction 
of  a  certain  proportion  of  oxygen  into  the  economy  is,  therefore,  the 
first  aim  of  the  function  of  respiration. 

The  general  tendency  of  the  various  gases  to  mingle  even  when 
wet  membranes  separate  them  has  been  pointed  out  in  "Osmosis/' 
Looked  at  in  its  essential  character,  the  respiration  of  animals  consists 
in  a  single  exchange  of  gases,  which  takes  place  during  the  action 
exercised  by  the  air  upon  the  blood.  In  fact,  atmospheric  oxygen, 
brought  into  contact  with  a  thin,  membranous  wall,  passes  through  it 
and  penetrates  the  blood,  while  the  carbonic-acid  gas  contained  in  that 
liquid  is  freed  from  it  through  the  same  membrane.  Therefore,  if 
respiration,  on  the  one  hand,  takes  something  away  from  the  blood,  on 
the  other,  it  communicates  to  it  a  principle  which  renders  it  suitable 
to  complete  the  organs,  furnish  material  for  their  secretions,  or  to 
repair  their  losses,  while,  at  the*  same  time,  giving  rise  to  a  disengage- 
ment of  heat  indispensable  to  the  free  exercise  of  the  functions.  It  is 
this  vivifying  principle  which  combines  with  the  organic  matters  of  the 
blood  to  form  the  water  and  carbonic  acid  that  are  unceasingly  elim- 
inated by  expiration  and  soon  decomposed  in  the  atmosphere  under 
the  influence  of  solar  radiation,  to  furnish  carbon  and  hydrogen  to 
vegetation. 

(237) 


238  PHYSIOLOGY. 

The  blood,  with  its  complex  constitution,,  becomes  in  this  way 
the  principal  medium  for  all  the  phenomena  of  nutrition.  It  is 
known  to  be  collecting,  in  its  course,  for  its  own  reconstitution,  certain 
materials  elaborated  by  the  digestive  passages  and  then  depositing 
assimilable  principles  in  the  various  tissues.  The  blood  represents, 
therefore,  a  reparatory  fluid  whose  continual  renewal  and  destruction, 
intrusted  to  digestion  and  respiration,  constitute  the  two  inseparable 
conditions  for  existence  of  the  higher  animals. 

When  air  is  fed  to  the  wood  in  the  firebox  of  a  boiler  a  process 
known  as  burning  takes  place.  It  is  a  real  chemical  process,  the 
oxygen  uniting  with  the  carbon  and  hydrogen  of  the  wood,  so  that 
both  the  wood  and  oxygen  disappear  as  such.  The  carbon  and  portion 
of  the  oxygen  unite  to  form  carbonic-acid  gas.  The  hydrogen  and 
the  remainder  of  the  oxygen  by  their  union  form  water.  The  two 
substances  thus  formed  pass  off  in  the  smoke,  leaving  behind  as  the 
debris,  or  ashes,  the  mineral  part  of  the  wood.  By  this  burning,  also 
termed  oxidation,  heat  and  a  flame  are  produced. 

Within  the  body  there  occurs  an  analogous  process,  also  termed 
oxidation,  whereby  the  oxygen  inhaled  into  the  body  slowly  burns  the 
protoplasm  of  cells  in  a  manner  similar  to  the  burning  of  the  wood  in 
the  boiler.  This  process  within  the  body  is  performed  so  slowly  that 
there  is  no  appearance  of  a  flame,  but  there  is  yielded  the  same  amount 
of  heat  as  would  be  produced  were  the  same  materials  burned  within  a 
furnace  or  stove.  Some  of  this  heat  is  utilized  to  give  warmth  to  the 
body,  while  the  remainder  of  it  is  converted  into  power  and  energy,  so 
that  the  body  may  do  work,  either  of  motion,  thought,  or  manufactur- 
ing the  various  products  of  the  body.  Oxidation  is  the  essential  process 
of  life,  for  when  it  ceases  life  ends.  It  occurs  in  every  cell  of  the 
economy.  Its  degree  in  the  living  cells  can  be  heightened  or  lowered 
according  to  the  needs  of  the  body.  The  end-products  of  body-oxida- 
tion are  also  carbonic-acid  gas,  water,  and  ashes,  or  urea  as  occurred 
in  furnace-oxidation. 

From  studies  in  general  physiology  it  is  known  that  that  pe- 
culiar form  of  energy  which  is  called  life  exists  only  in  association  with 
living  cells  or  living  organisms.  It  is*  liberated  only  during  a  catab- 
olism,  or  destructive  metabolism  of  living  cell-protoplasm,  and  which 
metabolism  is  possible  only  in  the  presence  of  oxygen.  During  these 
catabolic  metabolisms  the  living  protoplasm  of  the  cell,  the  deeply 
complex  protoplasmic  molecule,  is  split  up  into  two,  perhaps  more, 
simpler  molecules ;  these  last,  which  probably  represent  proteids,  may 
again  separate  into  still  simpler  ones.  Each  change  from  a  complex 


RESPIRATION.  239 

compound  to  a  simpler  one  leads  to  (1)  liberation  of  energy  upon 
which  depends  the  numerous  activities  of  life  and  (2)  to  a  new  com- 
bination of  the  simpler  molecules  with  oxygen.  Thus,  oxygen  is  the 
came  of  combustion,  but  the  complement  of  catabolism. 

Respiration  is  the  general  term  which  includes  all  of  those  activi- 
ties that  are  involved  in  the  furnishing  of  oxygen  to  the  tissues  of  a 
living  organism. 

The  respiratory  phenomena  do  not  exist  in  man  and  the  aerial 
vertebrates  only.  They  are  found,  of  the  most  varied  kinds,  in  all  of 
the  animal  species,  even  in  the  lowest;  these  last,  lacking  true  blood 
as  well  as  a  digestive  tube,  have  particular  juices  introduced  by  absorp- 
tion, the  nutritive  quality  of  which  can  develop  only  under  the  vivify- 
ing influence  of  atmospheric  oxygen.  It  may  here  be  added  that  the 
intervention  of  this  gas  is  as  indispensable  to  the  plant  as  the  animal 
in  all  periods  of  life.  The  sap,  analogous  to  the  blood,  cannot  be 
sufficiently  elaborated  and  become  a  really  nourishing  fluid  except  by 
the  oxygen. 

When  a  function  is  found  in  all  living  beings,  it  is  warrantable 
to  conclude  that  it  represents  one  of  the  fundamental  conditions  of 
their  existence.  Respiration  incontestably  offers  that  character.  Not 
only  do  all  living  species  breathe  at  their  different  ages,  but  they  cannot 
develop,  or  persist  in  their  development,  except  by  the  accomplishment 
of  that  function.  The  most  positive  experiments  have  demonstrated 
that  the  cell  of  the  plant  and  the  cell  of  the  animal  breathe,  one  in  the 
seed  and  the  other  in  the  egg  in  which  it  is  organized,  and  that  all 
development  is  arrested  as  soon  as  communication  with  the  atmospheric 
air  is  prohibited.  The  seed  absorbs  oxygen  from  the  air  for  the  benefit 
of  the  young  plant  that  it  contains,  fixes  some  traces  of  nitrogen,  and 
at  the  same  time  exhales  a  considerable  quantity  of  carbonic  acid. 

It  was  in  a  chicken's  egg  that  respiration  of  the  embryo  was  first 
recognized;  when  the  surface  of  the  egg  was  covered  with  an  im- 
pervious coating  of  oil  or  varnish,  the  embryo  failed  to  develop. 
Later  it  was  proved  that  the  egg  containing  a  chick  in  the  process  of 
development  also  absorbs  oxygen  and  exhales  carbonic  acid. 

The  life  of  mammals  shows  another  form  of  the  phenomenon :  In 
them  the  foetus,  by  reason  of  a  certain  union  of  his  vascular  appara- 
tuses, draws  from  the  blood  of  the  mother  the  necessary  oxygen  which 
his  pulmonary  surface  cannot  yet  supply  it  with  directly.  The  villi 
of  the  placenta,  plunged  into  the  vascular  sinuses  of  the  uterus,  effect 
a  kind  of  respiration  there. 


240  PHYSIOLOGY. 

THE  RESPIRATORY  APPARATUS. 

The  object  of  respiration  is  twofold,  viz. :  to  supply  Hie  oxygen 
necessary  for  the  numerous  oxidation  processes  that  are  constantly 
occurring  within  the  body,  as  well  as  to  remove  the  carbon  dioxide 
formed  within  the  body.  The  most  important  organs  for  this  purpose 
are  the  lungs  or  gills,  as  the  case  may  be,  though  it  must  never  be 
entertained  for  a  moment  that  they  are  the  special  seats  for  those 
combustion-processes  whereby  ensues  carbonic  acid  as  the  final  result. 
These  processes  occur  in  all  parts  of  the  body  in  the  substance  of  the 
tissues.  The  lungs  or  gills  are  merely  the  medium  for  the  exchange 
of  the  two  essential  gases.  For  this  interchange  it  becomes  necessary 
that  the  atmospheric  air  should  pass  into  them  and  that  the  changed 
air  should  be  expelled  from  them. 

In  essence  a  lung  or  gill  is  constructed  of  a  thin  membrane, 
whose  one  surface  is  exposed  to  the  air  or  water, — depending  upon  the 
species  of  animal, — while  on  the  other  surface  there  is  a  network  of 
blood-vessels,  the  separating  membrane  between  the  blood  and  aerating 
medium  being  the  thin  walls  of  the  small  blood-vessels  and  the  fine 
membrane  upon  which  they  are  distributed.  The  principle  is  always 
the  same  in  all  respiratory  apparatuses;  the  difference  between  the 
simplest  and  most  complicated  ones  is  one  of  degree  only. 

In  all  animals  in  which,  by  reason  of  their  complex  structure,  it 
becomes  necessary  to  have  special  arrangements  for  the  performance  of 
the  respiratory  function  it  is  found  that  the  act  is  divided  into  two 
stages :  (a)  an  external  respiration,  where  the  interchange  is  between 
the  air  or  water  and  the  circulating  medium  of  blood  as  it  passes 
through  richly  vascular  skin,  tracheae,  gills,  or  lungs ;  (b)  an  internal 
respiration,  which  is  an  interchange  between  the  blood  or  lymph  and 
the  cells  of  the  various  tissues  of  the  entire  body. 

Our  consideration  of  the  subject  will  confine  us  to  the  study  of 
the  human  respiratory  organs.  The  most  important  of  the  human 
apparatus  are  the  lungs,  which  are  contained  within  the  closed  chest, 
or  thorax,  having  no  communication  with  the  outside  except  through 
the  avenue  of  the  respiratory  passages. 

The  pulmonary  apparatus  consists  of:  (1)  the  air-passages — 
nose,  pharynx,  larynx,  trachea,  and  the  bronchi,  which  communicate 
with  the  lungs;  (2)  the  lungs  with  their  immense  number  of  small 
sacs,  known  as  the  air- vesicles ;  and  (3)  the  thorax.  The  accessory 
muscles  of  respiration,  when  called  into  play,  make  the  thorax  act 
as  a  bellows,  forcibly  causing  ingress  and  egress  of  air. 


RESPIRATION. 


241 


The  Air-passages. — The  very  first  portion  of  the  respiratory  pas- 
sageway, the  nose,  is  the  organ  of  the  special  sense  of  smell  and  will 
be  treated  in  detail  when  that  subject  is  discussed ;  the  anatomy  of  the 
pharynx  has  been  previously  noted  when  the  alimentary  canal  was 
under  attention.  The  larynx  is  placed  at  the  upper  part  of  the  pas- 
sage, being  a  dilatation  of  the  trachea.  It  is  the  cartilaginous  box 
which  contains  the  structures  concerned  in  the  production  of  voice. 
It  will  be  described  later  in  connection  with  that  function. 


Fig.  52. — Human  Respiratoiy  Apparatus.     (DuvAL.) 
It  shows  the  branching  of  the  bronchia  in  the  interior  of  the  lungs. 

The  Trachea  and  Bronchi. — The  trachea,  or  windpipe,  is  a  com- 
bined membranous  and  cartilaginous  cylindrical  tube,  flattened  pos- 
teriorly. Commencing  opposite  the  fifth  cervical  vertebra,  it  terminates 
by  dividing  into  two  bronchi  opposite  the  third  dorsal  vertebra.  Its 
length  is  about  four  inches,  its  breadth  (less  in  the  female  than  in  the 
male),  three-fourths  of  an  inch.  The  bronchi  diverge  from  the  trachea 
to  the  lungs  behind  the  great  blood-vessels  running  from  the  base  of 
the  cardiac  organ.  The  bronchus  on  the  right  side,  about  an  inch  in 
length,  runs  at  a  right  angle  to  the  root  of  the  lung  on  a  level  with 

16 


24:2  PHYSIOLOGY. 

the  fourth  dorsal  vertebra  and  posterior  to  the  right  pulmonary  artery. 
The  left  bronchus,  less  in  diameter  than  the  right,  but  about  twice  its 
length,  passes  downward  and  outward  beneath  the  arch  of  the  aorta 
to  the  root  of  its  corresponding  lung.  The  bronchi  and  trachea  are 
composed  of  a  series  of  cartilaginous  rings  lined  with  mucous  mem- 
brane. The  trachea  and  bronchi  are  encircled  by  the  cartilaginous 
rings,  which  are  not  closed  posteriorly  except  by  a  strong  fibro-elastic 
membrane,  and  contains  a  layer  of  pale  unstriped  muscular  fibers 
running  in  a  transverse  and  longitudinal  direction.  The  cartilaginous 
rings  preserve  the  caliber  of  the  trachea  and  bronchial  tubes.  The 
surface  of  the  tracheal  and  bronchial  mucous  membrane  is  smooth  and 
its  color  is  reddish  white.  Its  epithelium  is  of  the  ciliated  columnar 
form.  The  vibratory  movement  of  the  cilia — being  directed  upward — 
removes  dust  from  the  lungs.  Minute  glands  of  the  racemose  variety 
are  found  in  the  trachea  and  bronchi,  which  open  upon  the  surface. 
The  nerves  supplying  the  trachea  and  lungs  are  the  pneumogastric 
and  sympathetic. 

The  Lungs  are  in  the  thorax,  one  on  each  side,  separated  by  the 
heart  and  large  blood-vessels.  In  the  constantly  changing  diameters 
of  the  chest  they  accurately  fill  the  chest  which  contains  them.  They 
are  free,  and  attached  only  by  the  roots.  They  are  closely  invested 
with  a  serous  membrane,  the  pleura.  The  root  of  the  lung  is  placed 
near  its  mioMle  internally,  and  consists  of  the  bronchus,  pulmonary 
artery  and  veins,  the  blood-vessels  of  the  bronchia,  nerves,  and  lym- 
phatics, all  invested  with  a  reflection  of  pleura.  The  right  lung  has  its 
root  behind  the  superior  vena  cava.  The  root  of  the  left  lung  lies 
partly  beneath  the  arch  of  and  partly  in  front  of  the  descending  portion 
of  the  aorta.  In  the  root  of  the  right  lung  the  bronchus  is  the  highest ; 
in  the  root  of  the  left  lung  the  pulmonary  artery  is  the  highest.  The 
bronchi,  before  entering  a  depression  at  the  root  of  the  lungs,  the 
hilus,  subdivide,  the  right  into  three  branches,  the  left  into  two,  corre- 
sponding to  the  number  of  lobes  in  each  lung.  Each  lung  is  conical, 
with  a  broad,  concave  crest  resting  on  the  diaphragm  and  a  rounded 
apex  standing  above  the  level  of  the  first  rib  and  reaching  into  the 
neck.  Its  outer  surface  is  convex  and  its  inner  surface  is  concave 
and  faces  the  heart. 

The  weight  and  the  capacity  of  the  lungs  vary  according  to  many 
conditions.  Their  average  weight  is  about  two  and  one-half  pounds 
and  their  total  capacity  three  hundred  cubic  inches.  Their  long 
diameter  is  the  greatest  and  deepest  on  the  posterior  surface.  The 
right  lung  is  shorter  than  the  left,  but  wider  and  of  somewhat  greater 


RESPIRATION.  243 

bulk.  The  right  lung  has  three  lobes,  of  which  the  middle  one  is  the 
smallest  and  the  lowest  one  the  largest.  The  left  lung  has  two  lobes, 
of  which  the  lower  is  the  larger.  Between  the  lobes  of  the  left  lung 
in  front  there  exists  a  large  angular  notch,  corresponding  with  the 
position  at  which  the  impulse  of  the  heart  is  felt  against  the  walls 
of  the  chest. 

Normal  lung-tis.sue  always  shows  a  specific  gravity  less  than  that 
of  water;  consequently  it  will  float  when  thrown  into  water.  No 
other  tissue  does  this.  However,  should  lung-tissue  in  which  con- 
solidation has  resulted  from  some  disease  or  the  lung-tissue  from  a 
child  that  has  never  breathed  be  thus  tried,  it  will  sink  like  other 
tissues.  This  water-test  of  the  lungs  is  one  of  the  medico-legal  tests 
applied  to  ascertain  whether  a  child  found  dead  was  "stillborn"  or 
was  a  victim  of  infanticide. 

The  substance  of  the  lung  is  of  a  light,  porous,  spongy  texture, 
when  handled  crepitating  because  of  the  air  contained  in  its  tissue. 
Lung-tissue  is  very  highly  elastic;  it  completely  collapses  when  re- 
moved from  the  thorax  or  if  the  thoracic  walls  be  punctured  so  as  to 
admit  air  from  the  outside  into  the  pleural  cavity. 

In  color  the  lungs  are  pinkish  at  birth,  becoming  of  a  mottled  slate 
color  in  adult  life.  The  dark-colored  patches  are  produced  by  the  pres- 
ence of  carbonaceous  material  that  has  been  inhaled  and  deposited 
within  the  areolar  tissue  near  the  surface  of  the  organ.  The  carbon 
particles  are  absorbed  by  the  lymphatics,  being  carried  into  the  lym- 
phatic openings  by  the  leucocytes. 

Bronchi. — In  structure  the  bronchi  resemble  the  trachea.  In  the 
bronchi,  however,  there  are  unstriped  muscular  fibers  forming  the 
muscularis  mucosce,  while  the  cartilaginous  elements  are  scattered 
about  equally  in  all  parts  of  their  circumference. 

As  the  bronchi  are  traced  in  the  lungs  they  divide  into  tubes  of 
less  diameter.  These  again  subdivide  into  tubes  growing  smaller  in 
a  gradual  manner.  After  a  certain  stage  of  division  each  tube  is 
reduced  to  a  size  about  one-fiftieth  of  an  inch,  which  is  denominated 
a  bronchiole,  and  its  walls  are  lined  with  small  hemispherical  saccules 
called  alveoli,  or  air-cells.  These  bronchioles  then  open  into  a  blind 
space  called  infundibula,  which  are  lined  with  air-cells.  Near  the 
ending  of  the  bronchiole  with  the  infundibulum  the  former  ciliated 
epithelium  disappears  and  another  variety  of  epithelium  appears. 
This  new  variety  of  epithelium  consists  of  small,  flat,  polygonal 
nucleated  cells.  This  flat,  thin  epithelium  also  lies  over  the  blood- 
vessels and  even  extends  between  the  blood-vessels. 


244  PHYSIOLOGY. 

The  alveoli,  or  air-cells,  of  any  group  or  series  always  communi- 
cate with  one  another  to  open  by  a  common  orifice  into  a  terminal 
bronchus.  In  size  they  average  roughly  one  one-hundredth  of  an 
inch  in  diameter.  Form  is  given  to  the  air-cells  by  the  presence  of  a 
fine  membrane  of  slightly  fibrillated  connective  tissue  which  contains 
some  corpuscles.  This  is  closely  surrounded  by  a  great  many  fine, 
elastic  fibers  which  give  to  the  pulmonary  parenchyma  its  character- 
istic elasticity.  Some  nonstriped  muscular  fibers  are  apparent  in  the 
connective  tissue  between  the  cells ;  in  certain  diseases  these  become 
abnormally  developed.  The  number  of  alveoli  has  been  estimated  to 
be  seven  hundred  and  twenty-five  millions,  whose  superficial  area  is 
one  hundred  times  greater  than  that  of  the  body. 


Fig.  53. — Termination  of  a  Bronchus  in  an  Alveolus, 
a,  Bronchiole.     6,  Cavity  of  the  alveolus,     c,  Air-cells. 

Within  the  alveolar  walls  exists  a  dense  capillary  network.  They 
are  placed  more  toward  the  inner  side  of  the  vesicle,  being  covered 
only  by  the  thin  lining  of  the  air-sacs.  So  densely  are  they  arranged 
that  the  spaces  between  the  capillaries  are  even  narrower  than  the 
diameter  of  the  capillaries,  which  here  are  about  one  three-thousandth 
of  an  inch  in  diameter.  In  man  between  the  folds  of  two  adjacent 
alveoli  there  is  found  but  a  single  layer  of  capillaries,  while  on  the 
boundary  line  between  two  air-cells  the  course  of  the  capillaries  be- 
comes so  twisted  that  they  project  into  the  cavities  of  the  alveoli.  By 
these  arrangements  and  particularly  since  the  intervening  septa  are 
so  very  thin  and  permeable,  the  exposure  of  the  blood  to  the  air  becomes 
very  complete,  as  two  sides  of  a  capillary  are  thus  exposed  at  the 
same  time. 


RESPIRATION.  245 

Blood-supply, — The  lungs  receive  a  copious  supply  of  blood  from 
two  sources:  (1)  the  pulmonary  and  (2)  the  bronchial  arteries.  The 
bronchial  arteries  furnisli  nutriment  for  the  lung-tissues. 

The  Pleura. — Each  lung  is  enveloped  by  a  serous  membrane — the 
pleura — composed  of  two  layers,  one  of  which  is  closely  adherent  to 
the  external  surface  of  the  lung ;  the  other  adheres  to  the  inner  surface 
of  the  chest-wall.  These  layers  are  designated  visceral  and  parietal. 
The  visceral  pleura  envelops  the  lung,  while  the  parietal  pleura  lines 
the  thoracic  wall.  The  two  become  continuous  with  one  another  at 
the  root  of  the  lung. 

By  this  means  two  large  serous  sacs  are  formed,  each  distinct  and 
separate  from  the  other.  The  pleural  tissue  is  composed  of  a  layer 
of  fibrous  tissue  covered  with  endothelium.  During  health  the  two 
layers  of  the  pleura  are  always  in  contact  with  one  another,  just  enough 
fluid  being  present  between  them  to  allow  of  their  gliding  over  one 
another  with  but  very  little  friction  during  the  accomplishment  of 
the  respiratory  acts. 

Lymphatics. — These  are  very  numerous  in  lung-tissue  and  so 
arranged  as  to  form  several  systems. 

Nerves. — The  nervous  supply  of  the  lungs  is  from  the  anterior 
and  posterior  pulmonary  plexuses  derived  from  the  vagus  and  sympa- 
thetic. The  nerves  enter  the  lungs  to  follow  the  course  of  the  bronchi 
and  their  branches  and  end  in  the  unstriped  muscle. 

The  function  of  the  nonstriped  muscular  tissue  of  the  lungs  seems 
to  be  to  offer  a  general  resistance  to  increased  pressure  within  the  air- 
passages  as  may  occur  during  forced  expiration,  speaking,  singing, 
blowing,  etc.  The  vagus  is  the  nerve  which  supplies  motor  fibers  to 
these  muscle-fibers. 

MECHANISM  OF  RESPIRATION. 

If  respiration  be  suspended  for  but  a  very  short  while,  soon  there 
will  be  felt  a  lively  anxiety  due  to  the  nonsatisfaction  of  an  imperative 
need.  The  sensation  of  anxiey  is  produced  by  an  internal  sensation 
calling  for  need  of  breathing,  it  being  promptly  relieved  by  the  proper 
introduction  of  air  into  the  lungs.  When  the  air  inspired  and  retained 
becomes  unfit  for  further  oxidation,  there  arises  another  internal  sensa- 
tion which  calls  for  the  expulsion  of  that  same  air.  Each  respiratory 
time  is,  therefore,  preceded  by  a  particular  sensation  which  commands 
its  execution. 

These  two  movements  constitute,  by  their  regular  succession,  a 
complete  respiration,  the  purpose  of  which  is  to  maintain  in  the  lungs 


246  PHYSIOLOGY. 

regular  currents  which  serve  incessantly  to  renew  the  air  altered  by  its 
contact  with  the  blood.  The  mechanism  for  the  accomplishment  of 
respiration  consists  in  an  alternate  dilatation  and  contraction  of  the 
chest  by  means  of  which  air  is  drawn  into  or  expelled  from  the  lungs. 
These  two  acts  have  received  the  respective  names:  inspiration  and 
expiration.  As  is  known,  the  whole  external  surfaces  of  the  lungs  are 
in  direct  contact  in  an  air-tight  manner  with  the  inner  wall  of  the 
thorax,  so  that  the  lungs  must  be  distended  with  every  dilatation  of  the 
thoracic  wall  as  well  as  be  diminished  in  volume  by  every  contraction 
of  the  same  wall.  The  movements  of  the  lungs  are,  therefore,  for  the 
most  part,  passive,  being  dependent  upon  the  movements  of  the  thoracic 
wall.  This  close  approximation  of  lung  to  thoracic  wall  is  dependent 
upon  a  state  of  elastic  tension  maintained  within  the  lung,  due  to 
pressure  exerted  by  the  presence  in  the  lung  of  residual  air. 

From  these  data  it  becomes  evident  that  all  that  is  necessary  for 
the  production  of  inspiration  is  such  a  movement  of  the  walls  or 
diaphragm,  or  movement  of  the  two  synchronously,  that  the  capacity 
of  the  interior  should  be  increased.  By  reason  of  this  increase  there 
would  be  produced  a  temporary  vacuum  in  the  newly  acquired  space, 
or  at  least  a  great  diminution  of  pressure  within  the  lungs,  eo  that 
atmospheric  pressure  upon  the  outside  is  greater  than  that  within. 
Consequently  there  will  be  generated  a  current  of  air  proceeding  from 
the  outside  air  through  the  larynx  and  trachea  into  the  lungs  for  the 
purpose  of  equalizing  the  air-pressure  upon  the  inside  and  outside  of 
the  chest.  The  moment  this  point  is  reached  there  is  cessation  of  the 
current.  This  incoming  of  the  air  constitutes  the  first  of  the  two  acts 
of  respiration,  namely :  inspiration. 

For  the  expulsion  of  the  air  that  is  no  longer  fit  for  oxidation 
it  is  evident  that  there  must  be  a  reverse  movement  of  the  thoracic 
walls  whereby  the  chest-capacity  is  diminished.  This  act  increases 
the  pressure  exerted  by  the  contained  air,  with  the  result  that  as  much 
of  it  is  expelled  along  the  usual  avenues  for  its  passage  as  is  necessary 
to  equalize  the  pressure  upon  the  inside  and  outside  of  the  chest.  This 
outgoing  of  air  constitutes  the  second  act  of  respiration:  expiration. 
The  regular  succession  of  these  two  alternating  currents  of  air  con- 
stitutes breathing,  or  respiration. 

Inspiration. — Inspiration  has  for  its  motive  agents  the  diaphragm, 
the  scaleni,  external  intercostals,  the  sterno-cleido-mastoid,  the  angu- 
laris  scapula?,  the  small  pectoral,  the  serratus  magnus,  and  the  trapezius 
fibers,  with  the  great  pectoral.  All  of  these  muscles  by  their  contrac- 
tion directly  affect  the  expansion  of  the  chest,  with  the  exception  of  the 


RESPIRATION. 


247 


angularis  scapulae  and  trapezius,  whose  action  is  indirect.  The  dia- 
phragm is,  par  excellence,  the  muscle  of  inspiration ;  the  others  do  not 
contract  very  extensively  except  for  the  needs  of  labored  or  forced 
inspiration.  The  scaleni  are  confined  to  women  to  aid  inspiration  of 
the  superior  costal  type,  which  is  peculiar  to  the  sex. 

When  a  person  is  devoid  of  strong  emotions  or  not  engaged  in 
work  or  exercise,  the  breathing  is  quiet  and  regular.  It  is  then  said 
to  be  of  the  ordinary  type  and  is  principally  diaphragmatic  in  char- 
acter. 

When,  however,  the  breathing  is  extraordinary  in  type,  various 
other  muscles  are  called  into  action. 

The  size  of  the  chest-cavity  is  increased  in  (a)  its  vertical  diameter 
as  well  as  in  (b)  its  lateral  and  antero-posterior  diameters.  The  diam- 
eters are  ascertained  by  means  of  calipers. 


Fig.  54. — Diagrammatic  Representation  of  the  Action  of  the 
Diaphragm.     (BECLARD.) 

If  a  represents  a  plane  extending  in  expiration  from  the  sternum  to  the 
vertebra,  and  D  the  position  of  the  diaphragm  in  inspiration,  the  plane  a  will 
move  to  A,  while  the  diaphragm  will  descend  to  d. 

From  the  student's  study  of  anatomy  he  knows  that  the  diaphragm 
when  at  rest  and  in  a  state  of  relaxation  presents  the  general  form  of 
a  dome.  The  peak,  or  convexity,  of  the  dome  points  upward.  The 
student  also  knows  that  during  contraction  all  muscles  shorten  their 
fibers,  to  which  law  the  diaphragm  is  no  exception.  By  its  contraction 
the  convexity  of  the  dome  is  materially  diminished,  thereby  producing 
more  space  and  increasing  the  vertical  diameter.  This  helps  very 
materially  to  produce  a  vacuum  into  which  air  from  outside  of  the  body 
is  pushed  by  atmospheric  pressure.  That  is,  there  occurs  inspiration. 

The  diaphragm  is  supplied  by  the  phrenic  nerves. 

In  addition  to  the  diaphragm,  inspiration  is  aided  by  the  raising 
of  the  ribs  and  sternum.  Since  the  ribs  are  hinged  posteriorly  to  the 


248 


PHYSIOLOGY. 


vertebral  column,,  it  is  their  lateral  and  anterior  portions  which  possess 
the  most  motion;  that  is,  their  direction  is  slightly  forward  and 
upward. 

In  ascending,  the  ribs  straighten  upon  the  spinal  column,  and, 
instead  of  the  lower  ones  in  particular  being  so  oblique,  are  now  found 
to  occupy  a  more  nearly  horizontal  plane.  This  increases  the  antero- 


Fig.  55. — The  Action  of  the  Ribs  in  Man  in  Inspiration. 

The  shaded  parts  represent  the  positions  of  the  ribs  in  repose.  The  line 
A-B  represents  a  horizontal  plane  passing  through  the  sternal  extremity  of 
the  seventh  rib;  the  line  C-D  represents  a  horizontal  plane  touching  the 
superior  extremity  of  the  sternum;  the  line  H-G  indicates  the  linear  direc- 
tion of  the  sternum.  When  the  ribs  are  elevated  as  indicated  by  the  dotted 
lines,  the  line  A-B  becomes  the  plane  a-6,  the  line  C-D,  the  line  c-d,  and  the 
line  H-G  becomes  the  line  h-g,  the  projection  of  the  sternum  being  more 
marked  interiorly.  The  distance  which  separates  the  line  M-N  from  the  line 
m-n  measures  the  increase  in  the  antero-posterior  diameter  of  the  thorax. 

posterior  diameter.  At  the  same  time  that  the  ribs  are  raised  they 
undergo  a  movement  of  rotation,  by  virtue  of  which  they  separate 
from  the  median  line  of  the  chest.  It  is  this  movement  which  pro- 
duces an  enlargement  of  the  thorax  in  its  lateral  diameter  at  the  same 
time  the  antero-posterior  diameter  is  slightly  increased. 


RESPIRATION. 


249 


During  inspiration  the  ribs  are  raised,  when  the  breathing  is 
ordinary,  by  the  external  intercostals.  The  scaleni  and  costal  elevators 
also  are  of  service.  When  respiration  is  governed  by  the  latter  muscles, 
the  lower  part  of  the  chest  possesses  the  greater  expansion.  The 
reverse  is  true  when  inspiration  is  forced,  for  then  the  upper  antero- 
posterior  diameter  becomes  the  greater. 


I. 


Fig.  56. — Schema  of  Action  of  Intercostal  Muscles.     (LANDOIS.) 

I.  When  the  rods  a  and  6  which  represent  the  ribs  are  raised,  the  inter- 
costal space  must  be  widened  (e,  f  —  c,  d).    On  the  opposite  side  when  the 
rods  are  raised  the  line  g-h  is  shortened  (i,  k  —  g,  Ji),  the  direction  of  the 
external  intercostal,  l-m,  is  lengthened  (I,  m  —  o,  n)  in  the  direction  of  the 
internal  intercostals. 

II.  When  the  ribs  are  raised  the  intercartilaginei  indicated  by  g-h  and  the 
external  intercostals  indicated  by  l-k  are  shortened.  When  the  ribs  are  raised 
the   position    of   the    muscular   fibers    is    indicated    by   the    diagonals    of   the 
rhombs  becoming  shorter. 

During  extraordinary  inspiration — as  that  caused  by  violent  mus- 
cular exercise  or  when  some  pathological  condition  is  present  so  that 
air  finds  its  way  into  the  chest  only  as  the  result  of  strong  muscular 
effort — the  other  muscles  are  called  into  service. 

These,  the  emergency  muscles,  are  very  probably  the  sterno-cleido- 
mastoids,  the  serrati  magni,  the  pectorals,  and  the  trapezii. 


250  PHYSIOLOGY. 

Expiration. — Expiration,  when  it  is  effected  with  the  aid  of 
muscular  powers,  has  as  its  causative  agents  the  internal  intercostals, 
the  triangularis  sterni,  the  two  oblique  and  transverse  muscles  of  the 
abdomen,  and  quadratus  lumborum.  It  is  in  complex  expiration — as 
crying,  coughing,  singing,  expectoration,  sneezing,  etc. — that  the  pre- 
ceding muscles  enter  into  contraction.  The  abdominal  muscles  are 
the  most  powerful  in  the  above-named  group.  In  general,  it  may  be 
said  that  any  and  all  muscles  concerned  in  the  depression  of  the  ribs 
belong  to  the  expiratory  set  of  muscles. 

On  the  contrary,  ordinary  expiration  can  be  effected  by  the  mere 
relaxation  of  those  factors  concerned  in  the  production  of  inspiration. 
During  this  relaxation  the  thoracic  and  abdominal  walls,  by  reason 
of  their  elasticity,  compress  the  air-distended  lungs,  and  by  so  doing 
compel  expiration.  The  lung-tissue  itself  helps  to  the  extent  of  its 
own  elasticity.  The  expenditure  of  that  power  and  energy  necessary 
to  produce  inspiration  now  becomes  the  expiratory  exponent.  During 
ordinary  and  tranquil  breathing  this  elastic  recoil  of  the  stretched 
components  is  amply  sufficient  to  expel  the  air  from  the  lungs.  Thus 
no  muscular  energy  is  required  to  perform  expiration. 

A  normal  lung  is  never  able  to  contract  to  its  fullest  ability,  since 
it  is  always  distended  to  some  extent  by  reason  of  its  cohesive  attraction 
with  the  interior  of  the  chest-walls,  as  well  as  because  of  the  presence 
of  a  certain  proportion  of  air  within  the  vesicles  which  exerts  an 
expansive  pressure. 

It  is  interesting  to  note  that,  though  the  expiratory  muscles  be 
more  numerous  and  powerful  than  the  inspiratory  ones,  it  is  because 
the  former  are  intended  especially  for  complex  expiration;  that  is  to 
say,  violent  actions,  since  ordinary  expiration  is  able  to  be  effected  by 
the  mere  elasticity  of  the  parts.  During  expiration  the  lungs,  which 
were  dilated,  return  upon  themselves,  so  that  they  let  out  a  quantity 
of  air  nearly  corresponding  to  that  which  entered  at  first.  The  lungs, 
which  are  seen  to  be  entirely  passive  during  inspiration,  can  participate 
actively  in  expiration,  particularly  in  such  complex  acts  as  expectora- 
tion, coughing,  etc. 

There  are  various  modes  of  respiration  among  man  and  mammals 
which  are  usually  classed  under  three  principal  types.  In  the  abdom- 
inal type,  characteristic  among  children,  the  ribs  remain  motionless 
and  the  respiratory  action  is  revealed  only  by  the  movements  of  the 
abdominal  wall ;  this  becomes  projecting  during  inspiration  and  sinks 
during  expiration.  In  the  inferior  costal  type,  man's  type,  the  respira- 
tory movements  take  place  especially  at  the  level  of  the  lower  ribs, 


RESPIRATION. 


251 


beginning  with  the  seventh.  Finally,  in  the  superior  costal,  or  clavicu- 
lar, type,  the  respiratory  movements  are  very  manifest  only  about 
the  upper  ribs,  especially  the  first,  which  are  carried  upward  and  for- 
ward. The  clavicle  also  participates  in  this  movement.  This  last 
type  is  the  mode  of  respiration  peculiar  to  woman,  who  presents  it 
very  early.  The  state  of  pregnancy,  which  would  greatly  interfere 
with  the  other  types  of  respiration,  does  not  hinder  breathing  very 
much  in  this  last  type,  since  the  movements  take  place  naturally  at 
the  upper  part  of  the  chest. 

The  use  of  the  corset  counts  for  nothing  in  the  development  of 
this  mede  of  respiration  peculiar  to  women;  it  tends  merely  to  exag- 
gerate it.  The  superior  costal  type  is  found  perfectly  established  in 
girls  and  women  who  have  never  worn  this  kind  of  garment. 

Among  animals  the  abdominal  type  of  respiration  is  found  in  the 
horse,  cat,  and  rabbit,  and  the,  inferior  costal  type  in  the  dog. 


Fig.  57. — Tracing  of  a  Respiratory  Movement.     (FOSTER.) 

A  whole  respiratory  movement  is  comprised  between  a  and  a,  inspiration 
extending  from  a  to  6  and  expiration  from  6  to  a.  The  waves  at  c  are  caused 
by  heart-beats. 

The  Stethograph,  or  Pneumograph. — To  gain  an  exact  idea  of  the 
time  occupied  in  the  various  phases  of  respiration  it  becomes  necessary 
to  obtain  its  curve,  or  pneumatogram.  The  apparatus  for  recording 
these  respiratory  movements  is  termed  a  stethograph,  or  pneumo graph. 

The  simplest  form  of  stethograph  is  that  of  Brondgeest.  It  con- 
sists of  a  brass  saucer-shaped  vessel  covered  with  a  double  layer  of 
rubber  membrane.  The  air  is  forced  in  between  the  two  layers  until 
the  external  layer  bulges  outward.  This  is  placed  in  position  on  the 
chest  by  means  of  tapes.  The  cavity  of  the  saucer-shaped  apparatus 
communicates  with  a  recording  tambour,  which  writes  down  the  move- 
ments on  a  revolving  smoked  drum. 

The  resultant  curve,  known  as  the  pneumatogram,  shows  that  the 
acts  of  expansion  and  contraction  of  the  chest-wall  consume  nearly 
equal  times.  The  ascending  limb  (inspiration)  is  begun  with  mod- 


252 


PHYSIOLOGY. 


QJ 


Fig   58.  —  Marey's  Tym- 
panum and  Lever. 

(SANDERSON.  ) 

A,  Lever.  B,  Tympa- 
num. F,  Tube  wh  oh 
communicates  with  cavity 
of  the  tympanum  ami  con- 
nects with  the  tracheal 
cannula  or  the  card  o- 
graph. 


erate  rapidity,  becomes  accelerated  in  the  middle  of  its 
course,  to  be  again  slowed  at  its  end.  The  descending 
limb  (expiration)  shows  the  same  characteristics  as  to  its 
construction,,  thereby  giving  a  gradual  fall  to  the  curve. 

INSPIRATION  is  SLIGHTLY  SHORTER  THAN  EXPIRA- 
TION.— For  all  practical  purposes  it  may  be  stated  that 
the  average  respiratory  rhythm  is:  Inspiration  :  Expira- 
tion :  :  5  :  6.  However,  it  is  known  that  various 
authors  give  different  ratios,  and  in  women,  children,  and 
old  people  6  to  8  or  6  to  9  may  be  found.  Immediately  fol- 
lowing expiration  there  is  a  slight  pause. 

Cases  are  rather  rare  in  which  the  duration  of  in- 
spiration and  expiration  are  equal,  or  that  of  expiration 
shorter  than  inspiration.  When  the  respiratory  move- 
ments are  studied  as  depicted  on  the  pneumatogram,  it 
is  found  that  there  is  practically  no  pause  between  the 
end  of  inspiration  and  the  beginning  of  expiration. 

RESPIRATORY  SOUNDS. 

If  a  stethoscope  is  placed  over  a  portion  of  a  lung  at 
some  distance  away  from  the  trachea  and  larger 
bronchi,  a  sound  will  be  heard  the  character  of 
which  is  variously  described  as  soft  or  sighing, 
resembling  the  rustling  of  leaves  in  a  slight 
wind.  The  sound  is  heard  during  the  whole  of 
inspiration  and  is  followed  by  a  short  expiratory 
sound.  The  inspiratory  sound  is  three  times  the 
length  of  the  expiratory.  It  must  be  remem- 
bered that  the  movements  of  inspiration  are  to 
those  of  expiration  in  point  of  time  as  5  to  6, 
while  the  vesicular  sounds  of  inspiration  is  to 
expiration  as  3  to  1.  The  cause  of  vesicular 
sound,  according  to  one  theory,  is  supposed  to 
arise  from  the  passing  of  air  into  and  out  of  the 
alveoli  and  infundibula,  the  friction  here  gen- 
erating a  sound,  aided  by  the  sudden  dilatation 
of  the  air-vesicles. 

If  now  the  stethoscope  is  placed  over  the 
trachea  just  above  the  suprasternal  notch,  two 
sounds  are  heard:  one  during  inspiration,  the 
other  during  expiration.  They  are  of  equal 


RESPIRATION.  253 

length,  or,  if  anything,  the  expiratory  is  the  longer.  The  quality  of 
both  sounds  may  be  described  as  blowing,  tubular,  or  bronchial.  The 
expiratory  part  is  more  intense  and  frequently  of  higher  pitch.  This 
bronchial  sound  is  produced  by  air,  in  passing  through  the  chink  of 
the  glottis,  being  thrown  in  vibration  and  imparting  its  motion  to  the 
columns  of  air  in  the  trachea  and  bronchi. 

In  practical  medicine  it  is  inferred  that,  when  the  vesicular  mur- 
mur is  heard  over  any  portion  of  the  lung-tissue,  this  area  being  prop- 
erly distended,  the  lung  is  in  a  healthy  condition.  If,  however,  the 
expiratory  portion  of  it  becomes  loud  and  prolonged,  it  excites  inquiry. 

QUANTITY  OF  AIR  BREATHED. 

The  determination  of  the  volume  of  air  necessary  to  the  needs  of 
human  respiration  is  a  problem  that  has  received  much  attention. 
Because  of  a  multitude  of  circumstances,  both  external  as  well  as  those 
that  are  proper  to  the  individual  himself,  the  figures  representing  the 
quantity  of  air  that  enters  the  lungs  at  each  inspiration  and  the  quan- 
tity that  leaves  them  at  each  corresponding  expiration  can  scarcely 
have  more  than  an  approximate  value.  Nevertheless,  results  agreeing 
sufficiently  to  permit  of  establishing  an  average  of  the  quantity  of  air 
put  in  circulation  during  each  normal  respiratory  movement  has  been 
arrived  at.  It  is  very  generally  admitted  that,  in  an  adult  and  healthy 
man,  each  inspiration  introduces  into  the  pulmonary  apparatus  about 
20  cubic  inches  of  air. 

Among  the  numerous  observers  who  have  occupied  themselves  with 
the  study  of  the  quantity  of  air  put  into  circulation,  Herbst  and  Hutch- 
inson  may  be  cited  in  particular.  The  latter's  spirometer  is  the  instru- 
ment which  has  been  most  frequently  used  to  secure  data  in  experiments 
along  this  line.  It  represents  essentially  a  gasometer.  It  is  furnished 
with  a  fixed  scale  and  movable  indicator ;  the  latter  follows  the  move- 
ments of  the  air-receiver  to  indicate  them  on  the  graduated  scale. 
The  receiver  dips  into  a  reservoir  filled  with  water  and  communicates 
with  the  chest  of  the  experimenter  by  means  of  a  rubber  tube  ending 
in  a  glass  or  metal  funnel. 

To  measure  the  volume  of  air  concerned  in  exaggerated  respira- 
tion, the  experimenter  is  made  to  stand  up,  care  being  exercised  that 
his  chest  is  free  from  any  restraint  that  would  hinder  its  mobility. 
After  several  forceful  inspirations  and  expirations,  he  inhales  the 
greatest  quantity  of  air  that  he  can  draw  into  his  lungs.  With 
the  tube  of  the  spirometer  between  his  lips  he  then  makes  the  fullest 
possible  expiration. 


254  PHYSIOLOGY. 

By  subjecting  about  two  thousand  persons  to  this  test  Hutchinson 
recognized  that  the  quantity  of  air  which  a  maximum  inspiration  and 
expiration  can  put  into  circulation  varies  according  to  the  individual. 
It  is  230  cubic  inches  for  a  man  5  feet  8  inches  in  stature.  According 
to  this  observer,  the  prime  factor  in  producing  variance  in  pulmonary 
capacity  is  mainly  the  size  of  the  individual. 

For  every  inch  of  height  from  5  feet  to  6  feet,  8  additional  cubic 
inches  are  given  out  by  a  forceful  expiration  after  a  full  inspiration. 
Vice  versa,  for  every  inch  below  the  5-foot  mark  the  capacity  is 
diminished  by  the  same  amount. 

The  mobility  of  the  thoracic  walls  has  here  a  real  influence. 
Persons  with  narrow  chests  are  sometimes  found  who  can  dilate  the 
thorax  much  more  than  those  in  whom  the  circumference  of  that  part 
of  the  body  is  greater.  With  equal  dimensions,  the  number  indicated 
by  the  spirometer  increases  with  the  dilatability  of  the  thorax. 

The  individual's  capacity  appears  to  be  greatest  in  the  period  from 
the  twenty-fifth  to  the  fortieth  year,  showing  a  gradual  increase  until 
the  latter  mark  is  reached.  From  this  point  it  begins  to  diminish,  to 
become,  in  old  age,  less  than  it  was  even  in  youth. 

Observers  agree  in  admitting  that,  in  woman,  the  maximum  vol- 
ume expired  is  perceptibly  less  than  in  man.  The  difference  is  usually 
represented  by  50  cubic  inches.  Abdominal  tumors,  whatever  their 
nature  and  the  organ  affected,  have  the  constant  effect  of  diminishing 
the  volume  of  air  expired ;  pregnancy  alone  has  not  that  consequence. 

If  a  lung  from  an  animal  be  thrown  into  a  vessel  of  water,  it 
floats.  If  it  be  forcibly  submerged  and  then  squeezed,  bubbles  of 
air  will  find  their  way  to  the  water's  surface.  From  this  little  experi- 
ment the  student  knows  that,  even  though  the  lungs  be  collapsed, 
yet  they  contain  a  certain  amount  of  air  which  is  not  very  readily 
expelled.  This  is  the  air  which  is  held  within  the  confines  of  the 
small  alveoli  and  cannot  very  easily  find  its  way  through  the  small 
passageways  opening  into  them.  It  follows,  then,  that  all  of  the  air  in 
the  lungs  cannot  possibly  be  changed  during  each  respiration,  and  the 
amount  that  is  changed  bears  a  very  close  relationship  to  the  type 
of  respiration,  whether  it  be  forced  or  ordinary. 

1.  Tidal  Air.  —  The  volume  of  air  that  is  introduced  into  the 
lungs  during  ordinary  inspiration-  and  by  an  adult  in  good  health  is 
termed  tidal  air.  It  is  20  cubic  inches. 

The  tidal  air  finds  its  way  into  and  out  of  only  the  larger 
bronchial  vessels,  where  it  comes  into  contact  with  the  nearly  stationary 
columns  of  air  which  extend  through  the  smaller  bronchial  tubes. 


RESPIRATION.  255 

The  interchange  between  the  two  columns  is  by  a  process  of  diffusion. 
By  this  means  does  the  oxygen  find  its  way  to  the  blood  flowing  through 
the  capillaries,  while  the  carbonic  acid  makes  its  way  into  the  larger 
bronchial  tubes  to  be  finally  expelled  from  the  body. 

2.  Complemental  Air  is  the  quantity  of  air  which  we  are  able  to 
inspire  with  the  greatest  effort  over  and  above  that  of  ordinary  breath- 
ing.    The  average  is  estimated  by  volume  as  110  cubic  inches. 

3.  Reserved  Air,  or  supplemental  air,  is  the  quantity  of  air  re- 
maining in  the  lungs  after  an  ordinary  expiration  which  would  be 
expelled  by  the  fullest  effort.     It  is  considered  to  be  about  100  cubic 
inches. 

4.  Residual  Air  is  that  which  remains  in  the  lungs  after  the  fullest 
possible  expiration  and  canno(t  be  expelled  by  any  voluntary  effort. 
Its  volume  is  also  100  cubic  inches. 

5.  The  Vital  Capacity  is  the  tidal,  complemental,  and  reserved 
airs  added  together,  and  is  230  cubic  inches.     It  represents  the  amount 
of  air  which  a  person  is  able  to  expel  from  his  lungs  after  the  deepest 
possible  inspiration.     One-sixth  of  the  air  in  the  lungs  is  renewed 
at  each  ordinary  respiration. 

NUMBER  OF   RESPIRATIONS. 

In  an  adult,  the  number  of  respirations  per  minute  may  vary  from 
16  to  24.  It  is  usually  stated  that  4  pulse-beats  occur  during  each 
respiration.  The  number  is  varied  by  the  position  of  the  body ;  thus, 
there  may  be  counted  13  while  recumbent,  19  in  the  sitting  posture, 
and  22  respirations  per  minute  while  standing. 

During  infancy  and  childhood  the  number  of  respirations  is 
always  greater  than  in  the  adult.  Exercise  temporarily  increases  res- 
piration both  as  to  number  and  depth.  It  is  believed  that  there  is 
some  product  derived  from  the  metabolism  of  muscles  which  acts  as 
the  respiratory  stimulant. 

Every  athlete  knows  of  that  condition  popularly  termed  "second 
wind."  At  the  beginning  of  severe  exercise  there  is  a  marked  dyspnoea 
which  passes  away  after  a  short  time,  even  though  the  exercise  be  unin- 
terrupted. It  cannot  be  explained  physiologically,  but  is  believed  to 
be  in  a  very  great  measure  cardiac. 

Pathological. — Eespirations  may  be  increased  by  reason  of  fever, 
pleurisy,  pneumonia,  some  heart  diseases,  and  anaemia.  Diminution 
is  occasioned  by  pressure  upon  the  respiratory  center  in  the  medulla; 
this  occurs  in  coma. 


256  PHYSIOLOGY. 

PRESSURE  IN  THE  AIR=PASSAGES  DURING  RESPIRATION. 

It  has  been  previously  stated  that  even  after  the  deepest  expiration 
the  lungs  are  never  completely  collapsed.  They  are  still  "on  the 
stretch"  by  reason  of  the  elastic  fibers  contained  in  them.  These 
fibers,  acting  in  direct  opposition  to  the  external  atmospheric  pressure, 
diminish  the  amount  of  pressure  within  the  thoracic  cavity.  It  has 
been  found  that  in  man  the  elasticity  of  the  lungs  themselves  equals  6 
millimeters  of  mercury. 

The  reason  for  the  collapsing  of  the  lungs  when  the  chest  is 
opened  is  that  the  pressure  upon  the  pleural  and  alveolar  surfaces 
is  now  equal,  being  that  of  the  pressure  of  the  atmosphere.  The 
pressure  of  the  residual  air  was  sufficient  to  overcome  the  elasticity  of 
the  muscular  fibers  of  the  lungs.  As  long  as  the  chest-wall  was  un- 
opened the  lungs  contracted  only  until  their  elasticity  was  just  balanced 
by  the  outward  pressure  of  the  contained  air.  In  intra-uterine  life, 
and  in  stillborn  children  who  have  never  breathed,  the  lungs  are  com- 
pletely collapsed  (atelectasis).  If  the  lungs  be  once  inflated  they 
never  completely  collapse  so  long  as  the  thoracic  walls  be  not  pierced. 

When  a  manometer  was  attached  to  the  trachea  of  an  animal  so 
that  its  respirations  proceeded  unchecked,  every  inspiration  showed 
a  negative  pressure,  every  expiration  a  positive  pressure.  An  observer 
placed  a  U-shaped  manometer  tube  in  one  of  his  nostrils,  closed  his 
mouth,  let  the  other  nostril  open,  and  then  respired  quietly.  During 
every  inspiration  there  was  a  negative  pressure  of  1  millimeter  of 
mercury,  and  during  expiration  a  positive  pressure  of  from  2  to  3 
millimeters. 

Forced  respirations  produce  great  variations  from  the  above  fig- 
ures. The  greatest  negative  pressure  averaged  —  57  millimeters  of 
mercury  during  inspiration;  the  maximum  positive  pressure  during 
expiration  averaged  +  87  millimeters. 

The  greater  part  of  the  force  exerted  in  deep  inspiration  is  used 
in  overcoming  the  resistance  offered  by  the  elasticity  of  the  lungs,  the 
raising  of  the  weight  of  the  chest,  and  depressing  the  abdominal 
contents.  These  resisting  forces  acting  during  expiration  aid  the 
expiratory  muscles;  from  this  it  follows  that  the  forces  concerned 
in  inspiration  are  much  greater  than  those  of  expiration. 

Expiration  is  longer  and  stronger  than  inspiration,  but  the  sound 
of  inspiration  is  longer  than  that  of  expiration. 


RESPIRATION.  257 

THE  FUNCTION  OF  THE  UNSTRIPED  MUSCLE  OF  THE 
BRONCHIAL  SYSTEM. 

If  a  dog  be  curarized,  the  interior  of  a  small  bronchus  be  con- 
nected with  a  recording  instrument  (the  chest  being  opened),  and  a 
vagus  be  divided,  there  will  be  a  marked  expansion  of  the  bronchi. 
If  the  peripheral  end  of  the  vagus  be  stimulated,  then  a  strong  con- 
traction of  the  bronchus  will  ensue.  It  is  evident  here  that  the  smooth 
muscles  of  the  bronchi  are  under  the  influence  of  the  pneumogastrics. 
These  effects  could  also  be  called  out  in  a  reflex  manner.  This  ex- 
plains asthmas  due  to  reflex  irritations  transmitted  to  the  centers  of 
the  vagi.  Atropine  and  lobelina  paralyze  the  vagus  ending  in  the 
bronchial  muscles,  which  explains  their  utility  in  spasmodic  asthma. 

VARIOUS  FEATURES  OF  RESPIRATION. 

Nasal  Breathing. — During  ordinary,  quiet  breathing  most  people 
breathe  through  the  nostrils,  keeping  the  mouth  closed.  This  is  very 
proper  and  there  are  certain  advantages  to  be  derived  by  so  doing. 
Thus,  in  the  passage  of  the  air  through  the  nostrils,  whose  walls  are 
narrow  and  somewhat  tortuous,  the  air  is  not  only  warmed,  but  ren- 
dered moist  as  well.  By  this  means  there  is  prevented  the  irritation 
occasioned  by  cold,  dry  air  upon  the  lining  mucous  membrane.  In 
addition,  the  smaller  foreign  particles  are  caught  by  the  mucous 
lining  and  carried  outward  by  the  instrumentality  of  the  ciliated 
epithelium. 

Pathological. — Pulmonary  oedema,  which  is  a  transudation  of 
lymph  into  the  pulmonary  alveoli,  occurs  (1)  when  there  is  very  great 
resistance  to  the  blood-stream  in  the  aorta  and  its  branches;  (2) 
when  the  pulmonary  veins  are  occluded;  (3)  when  the  left  ventricle, 
owing  to  mechanical  injury,  ceases  to  beat,  while  the  right  ventricle 
continues  in  its  contraction. 

Injection  of  muscarine  rapidly  produces  pulmonary  oedema  by 
reason  of  increased  pressure  and  slowing  of  the  blood-stream  in  the 
pulmonary  capillaries.  The  effects  of  this  drug  are  counteracted  by 
atropine. 

Relation  of  Respiration  to  the  Nervous  System. — Movements  of 
respiration  are  entirely  dependent  upon  the  nervous  system.  They 
are  nicely  balanced  actions,  performed  by  voluntary  muscles  under 
the  guidance  of  a  special  presiding  nerve-center,  namely :  the  respira- 
tory center.  Through  its  influence  the  muscles  of  inspiration  and 
expiration  are  kept  working  rhythmically  and  regularly,  whether  the 


258  PHYSIOLOGY. 

individual  be  awake  or  sleeping.  There  are  constantly  proceeding 
from  the  center  co-ordinated  impulses  to  the  muscles  involved.  How- 
ever, the  muscles  being  voluntary,  they  may  be  controlled  momentarily 
by  the  will,  and  respiration  be  made  entirely  to  cease  for  a  minute  or 
two.  Soon  Nature's  cry  for  oxygen  becomes  so  strong  that  the  will 
is  overcome  and  respiration  is  begun  again  under  the  supervision  of 
the  respiratory  center. 

The  Respiratory  Center. — This  center  is  located  in  the  medulla 
oblongata,  in  the  formatio  reticularis,  behind  the  superficial  origin 
of  the  vagi  and  on  both  sides  of  the  posterior  aspect  of  the  apex 
of  the  calamus  scriptorius.  Flourens,  its  discoverer,  found  that,  when 
destroyed,  respiration  ceases  at  once  and  the  animal  dies.  Hence  he 
termed  it  "the  vital  knot."  It  is  a  bilateral  center;  that  is,  it  has  two 
functionally  symmetrical  halves,  one  on  each  side  of  the  median  raphe. 
If  separated  by  means  of  a  longitudinal  incision,  the  respiratory  move- 
ments continue  symmetrically  on  both  sides.  Destruction  of  one-half 
of  the  medulla  is  attended  with  paralysis  of  respiration  only  on  that 
side,  seeming  to  prove  that  each  half  of  the  center  is  particularly  con- 
cerned in  the  respiratory  muscles  of  its  own  side. 

During  ordinary  breathing  impulses  are  sent  from  the  respiratory 
center  along  the  phrenics  to  the  diaphragm  and  along  the  intercostal 
nerves  to  those  muscles  which  elevate  the  ribs.  Impulses  and  mes- 
sages to  the  center  find  their  way  along  the  fibers  of  the  vagi  nerves. 

While  it  seems  to  be  undisputed  that  the  principal  respiratory 
center  lies  in  the  medulla  and  upon  it  depends  the  rhythm  of  the 
respiratory  movements,  yet  there  have  been  found  other  and  sub- 
ordinate centers  located  in  the  cord.  These,  however,  are  reinforced 
by  the  main  one  in  the  medulla. 

The  cutaneous  nerves  also  exercise  some  effect  upon  respiration. 
The  most  marked  influence  is  exerted  by  those  of  the  face  (trigem- 
inus),  abdomen,  and  chest.  Both  thermal  and  mechanical  stimuli 
easily  excite  them. 

Mechanical  stimulation  of  the  sensory  nerves  is  sometimes  resorted 
to  by  midwives.  It  is  well  known  that  to  arouse  a  sluggish  respiratory 
center  they  resort  to  slapping  the  buttocks  of  a  newborn  child. 

During  the  act  of  deglutition  there  is  a  very  necessary  cessation 
of  breathing  for  a  short  period.  This  is  caused  by  stimulation  of  the 
central  end  of  the  glosso-pharyngeal  nerve. 

Section  of  the  cord  just  below  the  medulla  produces  an  arrest 
in  the  movements  of  not  only  the  intercostals,  but  even  the  diaphragm. 
Section  of  one  phrenic  nerve  paralyzes  the  corresponding  half  of  the 


RESPIRATION. 


259 


diaphragm;  division  of  both  nerves  causes  entire  cessation  of  move- 
ment of  the  diaphragm.  The  phrenic  nerves  take  an  active  part  in 
the  function  of  respiration.  When  these  nerves  are  bared  and  irritated 
there  is  noticed  a  rapid  movement  of  the  abdomen  produced  by  con- 
traction of  the  diaphragm.  The  spasmodic  movement  is  repeated  at 
each  irritation  so  long  as  the  tissue  of  the  nerve  remains  uninjured. 
If  instead  of  mechanical,  an  electrical  irritant  be  applied,  the  dia- 
phragm is  thrown  into  a  state  of  tetanic  contraction  and  produces 


Fig.  59. — Scheme  of  the  Chief  Respiratory  Nerves. 
after  Rutherford.) 


(LANDOIS, 


1X8,  Inspiratory  center.  EXP,  Expiratory  center.  Motor  nerves  are  in 
unbroken  lines;  expiratory  motor  nerves  to  abdominal  muscles,  AB;  to 
muscles  of  back,  DO;  inspiratory  motor  nerves,  phrenics  to  diaphragm,  Z). 
/A7T,  Intercostal  nerves.  RL,  Recurrent  laryngeal;  CX,  pulmonary  fibers  of 
vagus  that  excite  inspiratory  center.  CX',  Pulmonary  fibers  that  excite 
expiratory  center.  CX",  Fibers  of  superior  laryngeal  that  excite  expiratory 
center.  1NH,  Fibers  of  superior  laryngeal  that  inhibit  inspiratory  center. 

death  from  asphyxia.  As  the  irritability  of  the  phrenic  nerve  remains 
a  long  time  after  death,  it  becomes  easy  to  demonstrate  these  phe- 
nomena without  causing  any  pain. 

After  section  of  the  vagi  the  heart's  movements  become  more 
rapid  and  the  respirations  slower.  At  the  end  of  some  minutes  the 
nares  dilate  a  little,  inspiration  is  accompanied  with  a  slight  noise, 
an  indefinite  restlessness  seems  to  seize  upon  the  animal  from  head 
to  foot;  it  moves  about  frequently,  and  raises  and  lowers  the  head 
as  if  there  were  a  constriction  of  the  throat.  At  length  the  anxiety 


260  PHYSIOLOGY. 

of  the  animal  disappears;  it  is  calm  and  quiet;  respiration  is  slow 
and  the  beats  of  the  heart  augment  in  frequency.  Finally  the  animal 
dies  from  an  affection  of  the  lungs  known  as  vagus  pneumonia.  For 
a  time  after  the  section  the  amount  of  carbonic  acid  exhaled  and  of 
oxygen  taken  in  remain  the  same,  but  finally  they  are  much  changed. 
The  animals  usually  live  seven  days,  but  Pawlow  has  succeeded,  by 
dividing  one  vagus  and  then  waiting  some  time  before  dividing  the 
next  one,  in  keeping  them  alive. 

Instead  of  tying  or  dividing  the  vagi,  a  galvanic  current  may  be 
sent  through  them.  There  will  follow  disturbances  of  the  vascular 
system,  particularly  the  heart;  so  that  death  follows  in  a  short  time. 
If  the  central  end  of  a  divided  vagus  be  irritated  by  a  strong  induction 
current,  there  is  produced  a  strong  degree  of  excitation  in  the  medulla 
oblongata.  It  sends  out  impulses  along  motor  nerves  which  arrest 
respiration  in  a  state  of  inspiration,  due  to  tetanus  of  the  diaphragm. 


Fig.  60. — Arrest  of  Respiration  in  State  of  Expiration.     (IlEDOX.) 
By  irritation  of  the  central  end  of  the  vagus  in  a  chloralized  dog. 

Stimulation  of  the  central  end  of  the  superior  laryngeal  calls  out  an 
expiratory  arrest.  Each  half  of  the  respiratory  district,  termed  a 
center,  consists  of  two  minor  centers,  which  are  in  an  alternate  state 
of  activity.  The  one  center  is  inspiratory;  the  other,  expiratory. 
Each  one  forms  the  motor  central  point  for  the  acts  of  inspiration  and 
expiration.  The  co-ordinated  impulses  proceed  from  these  centers  in 
the  medulla  along  the  nerves  which  supply  the  muscles  of  respiration 
and  the  associated  muscles  of  the  face,  nose,  and  larynx. 

The  activity  of  the  respiratory  center  is  excited  by  irritation  of  the 
sensory  nerves,  either  cutaneous  or  pulmonary.  It  may  also  be  stimu- 
lated by  the  accumulation  of  carbonic  acid  in  the  blood,  producing 
dyspnoea;  diminution  of  oxygen  and  the  presence  of  heat  are  also 
noticeable  factors.  According  to  some  observers,  the  acid  substance 
formed  in  the  blood  when  the  muscles  are  greatly  exercised  also  stimu- 
lates the  inspiratory  center. 


RESPIRATION.  261 

The  functions  of  the  expiratory  center,  on  the  contrary,  are 
diminished  or  even  paralyzed  by  a  strong  excitation  of  the  sensory 
nerves.  Excess  of  oxygen  and  carbonic  acid  in  the  blood,  or  increased 
intracranial  pressure,  produce  similar  effects. 

The  consensus  of  opinion  among  physiologists  now  seems  to  be 
in  favor  of  considering  the  activities  of  the  respiratory  center  as 
purely  reflex,  and  that  the  vagus  is  the  principal  nerve  concerned 
in  the  reflex  activities. 

Hering  and  Breuer  put  animals  in  a  state  of  apnoea  by  repeatedly 
filling  the  lungs  with  air  by  a  bellows.  Then  when  the  chest  was 
greatly  distended  the  tracheal  cannula  was  closed  and  the  thorax  kept 
in  that  position.  The  first  movement  with  a  distended  chest  was  one 
of  expiration.  Then  after  the  animal  was  again  made  apnceic  by  re- 
peated insufflations,  the  air  was  sucked  out  of  the  chest,  the  tracheal 
cannula  closed,  and  the  chest  kept  in  that  position.  The  first  move- 
ment to  be  made  was  one  of  inspiration.  These  two  kinds  of  experi- 
ments show  that  dilatation  of  the  chest  irritates  the  fiber-ends  of  the 
vagus  in  the  lung,  which  carry  impulses  to  the  expiratory  center  to 
call  out  an  expiration.  The  collapse  of  the  lungs  shows  that  this  act 
excites  the  fiber-ends  of  the  vagus,  which  carry  impulses  to  the  inspira- 
tory  center  to  call  out  an  inspiration.  Hence  the  knowledge  that  in 
the  vagus  we  have  fibers  of  two  kinds :  one  calling  out  expiration  when 
an  ordinary  inspiration  is  made,  the  other  calling  out  inspiration  when 
an  ordinary  expiration  is  made.  So  that  every  act  of  inspiration  calls 
out  an  expiration  and  every  act  of  expiration  calls  out  an  inspiration. 

Apnoea. — When  a  dog  has  frequent  insufflations  of  air  through 
a  tracheal  cannula  by  means  of  a  bellows,  there  ensues  an  arrest  of 
respiratory  movements  for  a  short  time.  Eosenthal  believed  this  to 
be  due  to  an  excess  of  oxygen  in  the  blood  and  that  the  respiration 
centers  were  not  excited  because  of  this  excess  in  the  tissues.  Fred- 
ericque  lately,  by  cross-circulation  in  the  head  of  one  dog  with  blood 
from  another  dog,  has  been  able  to  produce  apnoea  which  remains  a 
long  time  if  the  other  dog  continues  to  receive  exaggerated  pulmonary 
insufflations.  This  apnoea  is  not  due  to  an  augmentation  of  the 
oxygen,  but  to  a  deficiency  of  carbonic  acid.  The  arrest  that  ensues  in 
a  dog  by  frequent  insufflation  of  hydrogen  instead  of  oxygen  is,  accord- 
ing to  Fredericque,  due  to  irritation  of  the  vagus  fibers,  which  call 
out  an  expiration-arrest  and  which  is  a  simulated  apnoea. 

Asphyxia. — In  considering  the  phenomena  of  asphyxia,  it  is  nec- 
essary to  distinguish  between  rapid  asphyxia,  produced  by  complete 
obstruction  to  the  entrance  of  air,  and  slow  asphyxia,  which  is  grad- 


262 


PHYSIOLOGY. 


i  sj>  g^Jaiojfsl.s 

r?   .S3  *  +»  be  >..=  is  _  ri 


RESPIRATION.  263 

ually  established.  The  phenomena  of  asphyxia  are  divisible  into  three 
stages,  which  are  easily  observed  in  animals,  especially  in  the  dog. 

In  the  first  stage,  which  lasts  about  a  minute,  the  phenomena  of 
dyspnoea  appear  in  the  beginning,  the  forced  inspiratory  movements 
are  very  marked,  especially  for  the  thoracic  muscles;  the  abdominal 
muscles  then  contract  forcibly.  At  the  end  of  the  first  minute  con- 
vulsions appear,  which  at  first  are  purely  expiratory  and  afterward 
accompanied  by  spasms,  more  or  less  irregular,  of  the  limbs,  especially 
the  flexor  muscles. 

In  the  second  stage,  which  lasts  about  the  same  length  of  time,  the 
convulsive  actions  cease,  sometimes  quite  suddenly;  the  expiratory 
movements  at  the  same  time  are  scarcely  perceptible,  the  pupil  is 
dilated,  the  eyelids  do  not  close  when  the  cornea  is  touched,  reflex 
actions  have  ceased,  all  the  muscles  except  the  inspiratory  are  in  a 
state  of  relaxation,  and  the  arterial  pressure  is  elevated.  In  fact, 
a  state  of  general  calm  ensues,  which  contrasts  forcibly  with  the 
agitation  of  the  first  stage. 

In  the  third  stage,  which  lasts  from  two  to  three  minutes,  the 
inspiratory  movements  become  more  feeble  and  widely  separated,  the 
extraordinary  muscles  of  inspiration  contract  spasmodically,  stretching 
convulsions  ensue,  and  opisthotonos  is  present.  The  nostrils  are  di- 
lated; convulsive,  yawning  movements  take  place;  and  death  closes 
the  scene. 

The  phenomena  of  slow  asphyxiation  follow  the  same  course,  but 
with  less  rapidity. 

CIRCULATORY  EFFECT  OF  ASPHYXIA. — The  circulation  does  not 
change  until  the  second  period  of  asphyxia.  During  the  convulsive 
stage,  and  particularly  toward  its  close,  the  heart  enlarges  to  double 
its  former  dimensions.  This  enlargement  is  due  to  the  lengthening  of 
the  diastolic  interval  and  to  the  quantity  of  blood  contained  in  the 
great  veins,  which,  in  fact,  are  so  distended  that,  if  cut,  they  spurt 
like  an  artery.  The  arterial  pressure  at  first  rises  and  then  falls  from 
160  millimeters  to  20  millimeters.  These  changes  are  explained  as 
follows :  The  increase  of  carbonic  acid  stimulates  the  vasoconstrictor 
center  and  thus  causes  general  contraction  of  the  arterioles.  The 
immediate  result  is  the  filling  of  the  venous  system,  in  the  production 
of  which  result  the  contraction  of  the  expiratory  muscles  of  the  trunk 
and  extremities  co-operate  powerfully.  The  heart,  being  abundantly 
supplied  with  blood,  fills  rapidly  during  diastole  and  contracts  vigor- 
ously. In  consequence  of  these  conditions  and  the  vasomotor  con- 
striction, the  arterial-  pressure  rises.  But  the  last  effect  is  only  tern- 


264  PHYSIOLOGY. 

porary;  the  cliastolic  intervals  are  lengthened  by  the  excitation  of  the 
vagus  center  by  the  carbon  dioxide,  the  vasomotor  center  is  paralyzed, 
and  the  weakness  of  the  heart  is  due  to  a  deficit  of  oxygen  in  the 
blood.  Then  the  heart  soon  passes  into  a  state  of  diastolic  relaxation 
and  greatly  enlarges.  Its  contractions  become  more  and  more  inef- 
fectual until  they  finally  cease,  leaving  the  arteries  empty,  the  veins 
full,  and  the  right  side  of  the  heart  engorged  with  blood. 

In  slow  asphyxia,  as  in  death  by  membranous  croup,  there  is  a 
feeling  of  painful  constriction  around  the  larynx  and  sternum,  yawns,, 
gapings,  and  vain  efforts  to  breathe,  with  dimness  of  sight,  buzzing  in 
ears,  and  vertigo,  soon  followed  by  loss  of  consciousness.  The  face  and 
lips  are  tumefied  and  livid;  the  eyes  watery  and  projecting;  the  con- 
junctiva injected;  the  jugular  veins  distended  with  blood;  the  nose,, 
ears,  hands,  and  feet  have  a  violet  color ;  the  whole  skin  presents  spots 
like  bruises;  the  heart  movements  are  uneven  and  intermittent, 
and  grow  weaker  and  weaker;  finally  the  respiratory  movements  be- 
come less  and  less  frequent,  soon  cease  altogether,  and  almost  at  once 
the  heart  stops  and  the  body  is  motionless  in  death. 

As  regards  mammals  particularly  the  age  affects  the  rapidity  of 
death  from  suffocation.  In  fact,  the  newborn  of  this  class  of  animals 
resist  the  suppression  of  respiration  very  much  longer  than  adults. 
This  accords  with  the  instances  of  newborn  infants  which,  having 
been  found  in  pools  of  water,  or  even  in  water-closets,  have  been  pre- 
served alive,  although  the  time  passed  since  their  immersion  permitted 
but  little  hope  of  saving  them. 

ARTIFICIAL  EESPIRATION  IN  ASPHYXIA. — In  cases  of  suspended 
animation  artificial  respiration  must  be  performed.  Care  should  be 
taken  first  to  remove  any  foreign  bodies  or  froth  from  the  mouth  and 
nose.  Draw  forward  the  patient's  tongue  and  keep  it  projecting 
beyond  the  teeth.  Eemove  all  tight  clothing  from  about  the  neck  and 
chest.  For  relieving  asphyxia  by  dilating  and  compressing  the  chest 
so  as  to  cause  an  exchange  of  gases  there  are  several  methods.  Chief 
among  these  are  Sylvester's  and  Marshall  HalFs. 

In  the  Sylvester  method  the  tongue  is  pulled  forward  to  prevent 
any  hindrance  to  the  entrance  of  the  air  into  the  windpipe.  Expan- 
sion of  the  chest  is  produced  by  drawing  the  arms  from  the  sides  of  the 
body  and  then  upward  until  they  almost  meet  over  the  head.  Bringing 
the  arms  down  to  the  sides  again,  causing  the  elbows  almost  to  meet 
over  the  pit  of  the  stomach,  produces  contraction  of  the  chest.  The 
rate  of  elevation  and  depression  of  the  arms  should  be  about  sixteen, 
times  per  minute. 


RESPIRATION.  265 

In  the  Marshall  Hall  method  the  person  is  placed  flat  upon  his 
face,  gentle  intermittent  pressure  being  made  upon  the  back  with  one's 
hands.  The  body  is  then  turned  on  the  side  and  a  little  beyond,  then 
upon  the  face  again,  and  the  same  pressure  continued  as  at  first.  The 
entire  body  must  be  worked  simultaneously,  the  same  number  and 
frequency  of  these  artificial  processes  of  respiration  being  employed 
as  in  the  Sylvester  method.  In  the  Laborde  method  rhythmical  trac- 
tion of  the  tongue  is  made. 

In  artificial  respiration  a  bellows  may  be  employed  in  a  gentle 
manner  so  as  not  to  rupture  the  lung. 

Modified  Respiratory  Movements. — As  to  breathe  is  to  live,  the 
modes  of  breathing  indicate  the  modes  of  life.  We  see  unfolded  in  a 
series  of  modifications  of  the  respiratory  act  many  of  the  sensations 
and  emotions  which  man  experiences  in  the  course  of  his  existence. 
His  birth  is  announced  by  a  cry,  which  seems  the  expression  of  a  first 
pain;  his  death  is  revealed  by  a  sigh  in  which  his  last  suffering  is 
breathed  out.  In  the  number  of  his  days  there  are  very  few  devoted 
to  laughter.  There  are  more  for  sobs.  Yawning  often  expresses  his 
weariness;  straining,  the  severity  of  his  labor;  sneezing,  coughing, 
and  expectoration  are  so  many  means  that  Nature  employs  to  struggle 
against  uncomfortable  or  painful  sensations.  ,  All  of  these  result  from 
modifications  of  respiration.  Hiccough  is  only  manifested  with  their 
aid.  Voice  or  speech,  the  supreme  attribute  of  man,  is  only  a  par- 
ticular mode  of  respiration. 

SIGHING. — A  large  inspiration,  slowly  executed  and  followed  by  a 
rapid  and  sonorous  expiration,  constitutes  the  sigh.  In  normal  condi- 
tions of  respiration,  in  about  every  five  or  six  inspirations  there  is  one 
which  is  longer  than  the  others;  it  is  really  a  slight  sigh.  It  is  sup- 
posed that  this  longer  inspiration  supervenes  whenever  oxidation  of 
blood  needs  to  be  accelerated.  It  takes  place  without  participation  of 
the  will;  in  fact,  it  is  one  of  those  movements  called  reflex.  The 
nervous  center  reacts  spontaneously  by  reason  of  a  painful  impression 
received  because  of  the  accumulation  of  the  venous  blood  in  the  right 
cavities  of  the  heart.  The  unpleasant  effect  of  sad  emotions  upon 
oxidation  of  blood  explains  why  sighs  are  given  at  such  times.  Their 
contagious  nature  is  due  entirely  to  sympathy. 

THE  YAWN  differs  from  the  sigh  more  by  its  mechanism  than 
by  its  causes  or  effects.  The  needs  of  oxidation  of  blood  call  it  forth 
in  the  same  manner  as  the  sigh  is  elicited.  But,  whereas  the  sigh  may 
be  voluntary,  the  yawn  is  always  involuntary.  It  is  not  easy  of  imita- 
tion, since  it  is  purely  reflex;  a  person  usually  will  not  yawn  if  the 


2G6  PHYSIOLOGY. 

need  of  doing  it  does  not  exist.  Besides  its  relation  to  oxidation,  it 
also  expresses  painful  sensations  .in  the  stomach,  hunger,  or  a  feeling 
of  torpor  at  the  approach  of  sleep. 

THE  HICCOUGH  cannot  be  compared  with  the  acts  connected  with 
respiration,  except  by  the  noise  accompanying  it.  It  is  a  spasmodic 
contraction,  abrupt  and  involuntary,  of  the  diaphragm  with  coincident 
contraction  of  the  glottis.  The  air,  drawn  rapidly  into  the  chest  by 
the  convulsive  contraction  of  the  diaphragm,  breaks  upon  the  out- 
stretched lips  of  the  glottis,  where  is  produced  the  sound  characteristic 
of  hiccough.  The  ordinary  causes  for  this  phenomenon  are  engendered 
in  the  stomach  by  the  too  rapid  introduction  of  alimentary  substances, 
by  alcoholic  drinks  or  those  charged  with  carbonic  acid,  and  by  certain 
foods.  It  can  also  result  from  a  special  state  of  the  nervous  centers. 

COUGHING  usually  arises  from  an  irritation  in  the  laryngeal  pas- 
sage ;  the  irritating  effect  of  the  sensory  filaments  of  the  larynx  reaches 
a  certain  intensity ;  there  is  then  a  deep  inspiration,  which  is  followed 
by  a  sudden  and  strong  expiration. 

Coughing  can  be  produced  voluntarily,  but  it  is  more  often  caused 
by  reflex  action,  which  it  is  generally  impossible  to  resist.  A  cold 
draught  on  the  skin  or  a  tickling  of  the  external  auditory  meatus  will 
provoke  a  cough  in  some  people. 

LAUGHING  and  SOBBING  have  this  feature  in  common :  they  have 
their  seat  in  the  chest  and  face  at  the  same  time.  They  act  especially 
upon  the  same  muscle:  the  diaphragm.  In  the  face  they  differ  in 
that  one  has  its  own  particular  seat  in  the  region  of  the  eye,  the  other 
around  the  mouth.  The  same  muscles,  the  same  nerves,  produce  sobs 
and  laughter.  Their  movements  of  inspiration  and  expiration  are, 
however,  accompanied  by  their  own  characteristic  sounds. 

SNORING  is  due  to  vibration  of  the  soft  palate. 

CHEYNE-STOKES  RESPIRATION. — This  is  a  peculiar  modification 
of  the  respiratory  movements  which  is  seen  in  certain  pathological  con- 
ditions, as  in  fatty  heart,  atheroma  of  the  aorta,  certain  apoplexies,  and 
in  uraemia.  It  has  even  been  noted  in  healthy  children  during  sleep. 
It  consists  of  respiratory  pauses  alternating  with  a  series  of  respira- 
tions till  a  maximum  depth  and  rapidity  is  reached ;  after  this  climax 
they  gradually  diminish  till  they  end  in  another  pause.  Certain 
drugs — -chloral  is  one — may  cause  Cheyne-Stokes  respiration. 

Cheyne-Stokes  respiration  rhythm  is  to  the  respiratory  system 
what  the  Traube-Hering  rhythm  is  to  the  circulatory  system.  Both 
arise  in  their  respective  centers  in  the  medulla  oblongata. 

The  pause  in  Cheyne-Stokes  respiration  is  somewhat  less  than 


RESPIRATION.  2G7 

half  of  the  duration  of  the  active  period.  During  the  pause  the 
pupils  are  contracted  and  inactitive;  when  respiration  begins  again 
they  become  dilated  and  sensitive  to  light.  The  eyeball  is  usually 
moved  at  the  same  time. 

CHEMISTRY  OF  RESPIRATION. 

Looked  at  from  a  chemical  point  of  view,  respiration  presents  the 
following  phenomena:  (1)  absorption  of  oxygen;  (2)  exhalation  of 
carbon  dioxide;  (3)  release  of  a  certain  quantity  of  nitrogen;  (4) 
exhalation  of  vapor  of  water. 

It  has  been  previously  stated  that  at  each  normal  respiration  of 
atmospheric  air  but  one-sixth  of  the  air  within  the  lungs  is  changed. 
This  current  does  not  actually  penetrate  beyond  the  largest  bronchial 
tubes.  The  air  which  finds  its  way  into  the  bronchioles  and  air- 
vesicles  does  so  by  diffusion. 

The  student  has  already  learned  that  the  normal  lung  contains 
within  it  a  certain  quantity  of  air  which  cannot  be  expelled  by  the 
strongest  expiration:  residual  air.  This  air  is  contained  within  the 
alveolar  air-spaces;  its  exchange  with  the  atmospheric  air  is  accom- 
plished by  the  slower  processes  of  gaseous  diffusion.  The  difference 
in  the  amount  and  pressure  of  the  two  gases — oxygen  and  carbonic- 
acid  gas — is  the  real  explanation  of  the  current-movement  of  the  two. 
The  C02  moves  outward,  the  0  inward.  The  interchange  is  aided 
by  the  heart-movements,,  also.  When  the  heart  contracts  (systole)  it 
occupies  less  space  in  the  thorax  than  it  does  during  relaxation 
(diastole).  Hence,  air  is  sucked  in  or  pushed  outward  through  the 
open  glottis  by  these  movements. 

A  glance  at  the  anatomy  of  lung-structure  reveals  the  fact  that 
the  alveoli  are  surrounded  by  a  dense  network  of  capillaries.  Some 
of  the  capillaries  even  project  into  the  air-spaces.  These  conditions 
make  more  easy  the  processes  of  diffusion. 

Some  of  the  oxygen  from  the  respired  air  passes  into  the  blood 
to  form  a  loose,  chemical  combination  with  the  haemoglobin  of  the 
red  corpuscles :  oxyhaBmoglobin.  This  gives  to  the  blood  its  red  color, 
making  it  arterial.  At  the  same  time  there  is  diffusion  of  carbonic 
acid  from  the  impure,  venous  blood  into  the  alveolar  compartments. 
Gradually  it  rises  in  the  air-vesicles  and  bronchioles  until  it  finds  its 
way  into  the  current  of  air  in  the  larger  bronchioles,  by  which  it  is 
expelled  from  the  system.  With  this  rise  of  carbonic  acid  in  the 
alveolar  air  there  js  a  corresponding  descent  of  oxygen  for  purposes 
of  oxygenation.  The  oxy haemoglobin  of  the  blood  is  carried  along 


268  PHYSIOLOGY. 

by  the  blood-stream  to  the  tissues  (the  real  seats  of  respiration),  where 
it  becomes  disengaged  to  unite  with  the  tissue-cells.  In  the  produc- 
tion of  heat  and  energy  it  has  united  with  the  carbon  of  the  tissues 
to  form  carbonic  acid  and  with  the  hydrogen  to  form  water.  That 
which  is  not  used  up  at  once  constitutes  a  reserve  supply  in  the  tissue  to 
be  used  as  occasion  demands. 

It  has  been  ascertained  that  the  quantity  of  oxygen  absorbed 
within  a  given  time  is  not  found  entirely  in  the  carbonic  acid  exhaled 
by  the  animal  during  the  same  time.  Consequently  one  can  scarcely 
consider  the  oxygen  as  employed  solely  in  burning  carbon  or  in  form- 
ing carbonic  acid.  Thus,  animals  draw  from  the  surrounding  atmos- 
pheric medium  a  quantity  of  free  oxygen  which  attacks  the  ternary 
and  quaternary  materials  of  the  organisms.  These  then  exhale  car- 
bonic acid  and  water  as  the  result  of  the  respiratory  combustion, 
together  with  a  small  quantity  of  nitrogen.  The  latter  proceeds  from 
the  destruction  of  a  certain  proportion  of  the  nitrogenized  substances 
of  the  blood  and  tissues.  As  an  animal  can  keep  its  weight  the  same 
during  these  combustive  changes,  it  must  be  admitted  that  the  carbon, 
hydrogen,  and  nitrogen  thus  lost  must  be  unceasingly  renewed  by  the 
food  it  ingests  and  digests. 

It  is  impossible  to  observe  any  constancy  in  the  quantity  of  the 
products  consumed  or  exhaled  while  searching  into  the  amounts  of 
oxygen  absorbed  and  carbonic  acid  given  off  by  man  in  a  certain  time. 
The  chemical  phenomena  of  respiration  are,  in  fact,  of  such  extreme 
changeableness,  due  to  the  variety  of  causes,  that  physiologists  can 
scarcely  know  them  all. 

The  expired  air  is  richer  in  C02  than  inspired.  It  contains  4.38 
volumes  per  cent,  of  this  gas,  and  consequently  a  hundred  times  more 
C02  than'the  air  inspired. 

The  air  expired  is  poorer  in  oxygen.  It  contains  16.03  volumes 
per  cent,  of  this  gas,  which  is  about  4.78  volumes  per  cent,  less  than 
the  inspired  air.  These  figures  show  that  the  absorption  or  loss  of 
oxygen  is  greater  than  the  elimination  of  C02.  This  further  sub- 
stantiates the  statement  that  all  of  the  oxygen  absorbed  does  not 
appear  in  the  form  of  carbonic  acid. 

So  often  in  the  study  of  physiology  the  student's  attention  is 
called  to  the  fact  that  the  movements  of  the  fluids  of  the  body  are 
always  in  the  direction  of  higher  to  lower  pressure.  The  explana- 
tion of  the  exchange  of  gases  held  in  loose  combination  in  the  blood 
and  those  comprising  the  atmospheric  air  in  the  lungs  is  another  inter- 
esting study  of  difference  of  pressure. 


RESPIRATION.  269 

The  exchange  depends  upon  the  law  of  "dissociation  of  gases/' 
and  is  as  follows:  "Many  gases  form  true  chemical  compounds  with 
other  bodies  when  the  contact  of  these  bodies  is  effected  under  such  con- 
ditions that  the  partial  pressure  of  the  gases  is  high.  The  chemical 
compound  formed  under  these  conditions  is  broken  up  whenever  the 
partial  pressure  is  diminished.,  or  when  it  reaches  a  certain  minimum 
level,  which  varies  with  the  nature  of  the  bodies  forming  the  com- 
pound. Thus,  by  alternately  increasing  and  decreasing  the  partial 
pressure,  a  chemical  compound  of  the  gas  may  be  formed  and  again 
broken  up."  (Landois.) 

The  C02  and  the  0  in  the  blood  form  certain  loose  combinations 
which  follow  this  law  exactly.  These  gaseous  compounds,  as  they  cir- 
culate with  the  blood-stream,  find  conditions  of  high  and  low  pressure 
enveloping  them,  whence  they  take  up  and  give  off  their  respective 
gases.  As  the  pressures  vary,  so  does  the  dissociation  of  the  gases. 

Thus,  the  oxygen-carrying  elements  of  the  blood,  the  haemoglobin 
of  the  red  corpuscles,  as  it  reaches  the  pulmonary  capillaries  is  poor  in 
0.  The  air  adjoining  them  in  the  pulmonary  alveoli  is  rich  with  0. 
The  low-pressure  hemoglobin  unites  with  the  high-pressure  0  to  form 
the  loose  compound  oxyhaamoglobin.  Later,  the  oxy haemoglobin  meets 
with  tissues  poor  in  oxygen  and  which  need  this  element  for  their 
combustion.  There  is  a  dissociation  from  a  higher  to  a  lower  pressure 
whereby  the  tissues  receive  their  needed  supply.  The  corpuscles  must 
needs  receive  replenishment  again  from  the  alveolar  oxygen,  and  in 
this  way  the  circle  is  completed. 

On  the  other  hand,  the  blood  in  contact  with  the  body-tissues 
meets  a  high  pressure  of  C02.  By  reason  of  which  compounds  are 
formed  containing  C02,  in  which  form  they  reach  the  air- vesicles  in 
the  lungs.  The  inspired  air  contained  within  the  air-vesicles  has  a 
much  lower  partial  of  C02  than  that  contained  in  the  venous  blood 
coming  from  the  tissues.  Hence,  the  dissociation  of  the  C02  from  the 
blood  to  the  vesicular  air,  finally  to  make  its  exit  along  the  bronchioles, 
bronchi,  trachea,  etc.,  to  the  atmosphere.  Bohr,  of  Copenhagen,  be- 
lieves the  epithelial  cells  of  the  air-cells  have  the  power  to  excrete 
carbonic  acid  and  absorb  oxygen  independent  of  the  differences  in 
tension  of  the  gases. 

The  temperature  of  the  air  expired  is  greater  than  that  of  the  air 
inspired,  and  is  but  a  trifle  lower  than  the  body-temperature.  Though 
the  temperature  of  the  surrounding  atmosphere  vary,  that  of  the  ex- 
pired air  remains  nearly  the  same. 


270  PHYSIOLOGY. 

The  volume  of  the  air  expired  is  greater  than  that  of  the  air 
inspired,  by  reason  of  the  increase  in  temperature  and  the  contained 
watery  vapor.  If,  however,  it  be  dried  and  reduced  to  the  same  tem- 
perature as  the  inspired  air,  there  will  be  a  diminution  of  volume: 
about  one-fiftieth. 

The  respiratory  quotient  is  the  relation  between  the  volume 
of  oxygen  absorbed  and  the  volume  of  carbonic  acid  eliminated. 
That  is  :— 

volume  of  C02  given  off 

The  respiratory  quotient  =—  — .     Normally  it  is 

volume  of  0  absorbed 

4  38 

about——  =  0.9. 
4.78 

This  quotient  varies,  however,  with  the  nature  of  the  chemical 
composition  of  the  foods  ingested.  With  the  hydrocarbons  the  quotient 
approaches  unity.  The  carbohydrates  contain  in  their  molecules 
enough  oxygen  to  oxidize  their  hydrogen;  all  that  remains  for  the 
inspired  oxygen  is  to  burn  up  the  carbon.  The  fats  and  albumins, 
on  the  contrary,  possess  too  little  oxygen  to  burn  all  of  the  hydrogen 
and  nitrogen  they  contain.  Hence  all  of  the  oxygen  is  not  found  in 
the  C02  eliminated,  and  the  respiratory  quotient  falls  to  0.75.  On  a 
mixed  diet  the  quotient  is  intermediate  between  0.9  and  0.75.  In 
plants  the  respiratory  quotient,  especially  in  starchy  ones,  is  equal 
to  1.0.  In  fatty  seeds  the  respiratory  quotient  is  0.6  to  0.8. 

Muscular  activity  augments  the  gaseous  exchanges  and  so  makes 
the  respiratory  quotient  approach  a  unit.  All  things  being  equal,  a 
man  absorbs  more  oxygen  and  exhales  more  carbonic  acid  than  a 
woman.  The  exchanges  are  increased  in  the  latter  during  pregnancy. 

During  sleep  the  consumption  of  oxygen  and  the  elimination  of 
C02  diminish  about  one-fourth.  This  decrease  depends  upon  mus- 
cular and  intellectual  repose,  darkness,  etc.  The  cells  of  the  tissues 
determine  the  amount  of  oxygen  needed,  and  not  an  excess  of  the 
oxygen  present.  The  intramolecular  changes  take  place  in  the  cells 
of  the  tissue,  and  not  in  the  blood.  The  amount  of  water  thrown 
off  daily  is  about  a  pound;  of  oxygen  taken  in,  about  a  pound  and 
one-half;  and  of  carbonic  acid  thrown  off,  a  little  more  than  a  pound 
and  a  half. 

In  human  blood  the  average  total  gases  are  estimated  to  be,  in 
round  numbers,  60  volumes  per  cent,  at  0°  C.  and  760  millimeters' 
pressure,  made  up  as  follows: — • 


RESPIRATION.  271 

ARTERIAL  VKNOTS 

BLOOD.  BLOOD. 

Oxygen   20  8  to  12 

Nitrogen    1.4  1.4 

Carbonic  acid  39  46 

The  above  table  represents  the  average  composition  of  the  gases 
contained  in  man's  blood. 

A  considerable  attraction  exists  between  the  particles  of  solid, 
porous  bodies  and  gases,  whereby  the  latter  are  condensed  within  the 
pores  of  the  solid  bodies;  that  is,  the  gases  are  absorbed.  Fluids  can 
also  absorb  gases.  One  of  the  functions  of  the  blood  is  to  carry  oxygen 
from  the  lungs  to  the  tissues  and  carbon  dioxide  from  the  tissues  back 
to  the  lungs  for  expulsion  from  the  economy.  These  two  gases,  to- 
gether with  nitrogen,  present  themselves  in  two  different  states  in  the 
blood.  The  blood,  a  fluid,  must  very  naturally  absorb  gases  also. 
Hence  one  would  expect  to  find  0,  C02,  and  N  held  in  solution,  and 
that  these  gases  should  behave  according  to  Dalton's  law :  the  amount 
of  gas  dissolved  in  a  liquid  varies  with  the  pressure  of  the  gas;  the 
higher  the  pressure,  the  greater  the  amount  of  gas  dissolved.  But 
oxygen  held  in  the  blood  disregards  Dalton's  law,  since  its  proportions 
in  the  blood  in  various  parts  of  the  body  remain  fairly  constant  no 
matter  what  the  pressure.  Hence,  it  owes  its  presence  in  and  obeys 
laws  dependent  upon  its  being  in  the  form  of  loose  chemical  combina- 
tions. If  the  oxygen  were  mainly  held  in  solution,  then  would  the 
blood  give  it  up  in  a  forming  vacuum  in  direct  proportion  to  the  falling 
oxygen-pressure.  That  these  conditions  do  not  follow  tends  to  estab- 
lish the  fact  that  the  oxygen  is  held  by  some  chemical  union.  Experi- 
mental physiologists  also  tell  us  that  in  their  work  they  notice  that 
very  little  0  is  given  off  in  a  forming  vacuum  until  a  very  much  re- 
duced pressure  is  reached,  when  there  is  a  sudden  evolution  of  the  gas, 
just  as  though  it  had  been  freed  from  some  restraining  influence.  The 
restraint  is  now  generally  accepted  to  be  the  chemical  union  before 
mentioned. 

Physiologists  admit  to-day  that  the  major  portion  of  the  oxygen 
of  the  blood  is  contained  in  the  red  corpuscles,  which  are  the  special 
messengers  for  carrying  it  to  the  different  tissues.  Their  capacity 
for  holding  oxygen  is  nicely  demonstrated  by  the  following  simple 
experiment :  Serum,  without  corpuscles,  is  agitated  in  the  presence  of 
oxygen.  The  amount  of  oxygen  absorbed  is  found  to  be  less  than  half 
what  would  be  taken  up  by  the  same  amount  of  serum  containing  red 
corpuscles. 


272  PHYSIOLOGY. 

The  oxygen,  being  preferably  united  with  the  corpuscles,  is  joined 
to  them  in  a  very  unstable  combination.  The  affinity  is  just  strong 
enough  to  facilitate  the  conveyance  of  the  gas  in  the  circulatory  system, 
yet  not  so  strong  but  that  it  may  attack  the  combustible  materials  of 
the  tissues.  Oxygen  united  chemically  with  haemoglobin  forms  oxy- 
haemoglobin. 

However,  it  must  be  kept  in  mind  that  some  of  the  oxygen  is  con- 
tained in  the  blood-plasma,  where  it  is  in  simple  solution  and  obeys 
the  laws  of  Dalton. 

There  can  scarcely  be  any  doubt  of  the  source  of  the  oxygen  con- 
tained in  the  blood,  for  it  evidently  comes  from  the  atmospheric  air, 
of  which  it  forms  one  of  the  elements.  It  represents  the  indispensable 
agent  of  most  of  the  transformations  which  take  place  in  the  heart  of 
the  general  economy. 

Ehrlich's  experiments  with  methylene  blue  and  other  similar  pig- 
ments show  the  intense  affinity  of  the  tissues  for  oxj^gen. 

Relation  of  C02  in  the  Blood. — Carbonic  acid  must  be  regarded, 
on  the  contrary,  as  one  of  the  final  products  of  the  nutritive  transmu- 
tations. It  is  destined  to  be  eliminated  with  the  vapor  of  water  and 
free  nitrogen,  especially  through  the  respiratory  passages.  When  the 
very  small  proportion  of  this  gas  in  ordinary  atmospheric  air  and  its 
considerable  amount  in  expired  air  are  considered,  it  is  easy  to  be  con- 
vinced that  carbonic  acid  is  indeed  a  product  of  the  organism.  The 
gas,  therefore,  comes  from  the  tissues  and  liquids  themselves  of  ani- 
mals, and  not  from  outside  media. 

It  is  very  generally  admitted  that  the  greater  part  of  the  carbonic 
acid  is  in  a  condition  of  chemical  combination.  The  principal  com- 
pound is  bicarbonate  of  sodium. 

The  tension  of  the  carbonic  acid  in  the  tissues  is  high.  It  is  less 
in  the  alveolar  air.  Hence  we  find  it  working  its  way  along  the 
respiratory  passages  to  be  expelled  by  the  movements  of  respiration. 
The  movement  of  the  oxygen  was  found  to  be  toward  the  tissues ;  the 
direction  of  carbon  dioxide  is  the  reverse :  away  from  the  seats  of 
tissue-combustion. 

It  has  been  found  that,  when  the  lung  is  distended,  the  heart 
beats  faster,  this  increased  action  being  caused  by  an  irritation  of  the 
sensory  nerves  in  the  lungs,  which,  in  a  reflex  manner,  inhibits 
the  cardio-inhibitory  center  and  allows  the  heart  to  beat  faster  as  the 
brake  is  taken  off. 

Dr.  Da  Costa,  in  his  examination  of  twenty-four  glass-blowers, 
found  that  in  eleven  the  pulse  ranged  from  90  to  116  per  minute. 


RESPIRATION.  273 

I  have  shown  elsewhere  that  this  is  due  to  the  irritation  of  the  sensory 
fibers  by  the  great  distension  of  the  lungs  diminishing  the  irritability 
of  the  cardio-inhibitory  center,  since  the  great  lung-distension  occurs 
daily  for  years. 

Now,  it  is  well  known  that  the  inhibitory  power  of  the  vagus  in 
man  is  very  great,  and  its  power  varies  in  different  individuals,  which 
would  explain  why  the  thirteen  other  glass-blowers  showed  no  habitual 
acceleration  of  the  heart.  As  this  performance  is  kept  up  many  hours 
daily  for  a  series  of  years,  it  is  easy  to  conceive  that  the  cardio- 
inhibitory  power  of  the  vagus  centers  receives  such  a  diminution  of 
irritability  so  often  that  it  would  at  length  remain  constantly  weak. 

The  vasomotor  center  also  sends  out  rhythmical  impulses  by 
which  undulations  of  blood-pressure  are  produced.  That  this  center 
is  capable  of  producing  such  undulations  has  been  amply  verified  by 
the  existence  of  the  Traube-Hering  curves. 

Respiration  of  Different  Gases. — Eespiration  is  essentially  the 
intaking  of  oxygen  and  the  output  of  carbon  dioxide  by  the  living 
cells.  Among  the  higher  orders  of  animals  two  phases  of  respiration 
are  distinguished — the  external,  the  exchange  of  gases  between  the  air 
or  water  and  the  blood;  and  the  internal,  the  exchange  between  the 
blood,  lymph,  and  the  tissues. 

The  usual  and  normal  medium  inspired  is  ordinary  atmospheric 
air,  from  which  there  is  derived  the  needful  supply  of  oxygen.  The 
open  atmosphere  is  a  mixture  of  gases  in  the  following  approximate 
proportions : — 

(Nitrogen,  including  argon,  etc 79.00  ^ 
Oxygen    .                                                           .   20.96    L  in  100  parts. 
Carbon  dioxide  0.04  J 
NH8,  H20,  and  organic  matter  in  small  variable  quantities. 

Though  the  quantity  of  water  in  the  air  is  marked, — over  1  per 
cent., — it  is  not  customary  to  reckon  it  in  the  gaseous  constituents. 

Some  gases,  as  hydrogen  and  nitrogen,  produce  no  specific  effects 
from  any  toxic  powers  in  themselves  when  they  are  breathed;  they 
produce  results  simply  because  they  exclude  the  proper  supply  of 
oxygen  for  the  animal.  On  the  other  hand,  gases  such  as  carbon 
dioxide,  carbon  monoxide,  nitrous  oxide,  and  hydrogen  sulphide,  when 
respired  in  sufficient  bulk,  are  absorbed  and  so  produce  specific,  toxic 
effects.  A  third  class  of  gases,  as  ammonia  and  nitric  oxide,  are  not 
respirable  because  of  their  highly  irritant  action  upon  the  respiratory 
apparatus,  spasm  of  the  glottis  being  produced. 


274  PHYSIOLOGY. 

Carbpn  dioxide,  when  undiluted,  is  irrespirable  by  reason  of  the 
spasm  of  the  glottis  occasioned.  Properly  diluted  it  can  be  respired, 
but  produces  headache,  dizziness,  drowsiness,  and  dypsncea  by  an 
action  on  the  nervous  system.  Nitrous  oxide  acts  directly  upon  the 
nervous  system,  partly  by  a  special  action  and  partly  by  producing  an 
excess  of  C02  in  the  blood.  Nitrogen  and  hydrogen  gases  produce 
their  fatal  effects  by  asphyxia,  due  to  exclusion  of  the  oxygen  and 
thereby  preventing  oxygenation  of  the  blood-corpuscles.  Differing 
from  these  gases  are  the  effects  produced  by  inhalation  of  carbon 
monoxide.  It  was  long  known  that  this  gas  was  poisonous,  but  it 
has  only  been  within  recent  years  that  its  mode  of  producing  asphyxia 
has  been  learned.  Instead  of  excluding  the  oxygen,  it  displaces  the 
latter  in  the  blood,  forming  a  very  stable  compound  with  the  hemo- 
globin of  the  red  corpuscles.  It  is  interesting  to  note  that  the  color 
of  the  blood  after  death  from  asphyxia  from  carbon  monoxide  is 
cherry-red;  in  other  forms  of  asphyxia  the  blood  is  almost  black. 
The  action  of  this  gas  is  of  practical  importance,  since  every  year  it  is 
the  cause  of  many  deaths.  They  occur  from  poisoning  with  coal-gas 
(especially  where  charcoal  stoves  are  used  in  small  rooms),  the  fumes 
of  kilns  and  coke-fires,  and  from  inhaling  the  air  of  coal-mines,  espe- 
cially after  explosions. 

Caissons  and  the  Effect  of  Compressed  Air. — Men  are  able  in 
caissons  to  support  during  some  moments  a  pressure  of  five  to  ten 
atmospheres  when  they  proceed  with  caution.  If  the  pressure  is  .too 
rapid  there  is  great  danger.  If  an  animal  who  resists  a  pressure  of 
ten  atmospheres  dies  instantly  from  a  rapid  change  to  ordinary  pres- 
sure, the  autopsy  shows  that  the  heart  and  large  vessels  are  filled 
with  bubbles  of  gas,  especially  of  nitrogen.  Under  the  influence 
of  double  or  treble  pressure  the  blood  absorbs  a  double  or  triple  pro- 
portion of  air,  especially  the  nitrogen.  If  the  animal  is  submitted  to 
a  rapid  diminution  of  pressure,  the  nitrogen,  not  being  kept  in  solu- 
tion in  the  blood,  is  disengaged  in  a  gaseous  state  in  the  form  of 
bubbles,  which  produces  embolism  in  the  capillaries  of  the  brain,  lungs, 
and  heart,  and  which  arrests  the  circulation.  To  avoid  the  disen- 
gagement of  bubbles  of  nitrogen  it  is  necessary  to  let  the  atmospheric 
compression  down  in  a  very  gradual  manner.  Operatives  in  leaving 
the  tubes  in  which  compressed  air  exists  must  remain  a  quarter  to  a 
half  hour  in  the  closed  chambers,  where  the  pressure  is  reduced  little 
by  little.  The  excess  of  gas  absorbed  is  slowly  eliminated  by  the  lungs 
without  producing  an  accident.  Four  atmospheres  is  about  the  amount 
that  operatives  can  work  in  with  safety.  Every  ten  meters  in  depth  of 


RESPIRATION.  275 

water  roughly  equals  one  atmosphere.  By  itself  compressed  oxygen  is 
a  toxic  agent,  for  it  lowers  the  output  of  carbonic  acid  and  the  tem- 
perature of  the  body.  The  cure  for  caisson-paralysis  is  recompression 
and  slow  decompression. 

Rarefied  Air. — All  travelers  who  have  climbed  the  Alps  speak  of 
the  same  troubles  experienced  by  them  at  nearly  the  same  altitude :  a 
considerable  diminution  of  appetite,  a  disgust  for  food,  nausea  and 
even  vomiting,  palpitations,  headache,  lassitude,  sleepiness,  and  buzzing 
in  the  ears.  This  state  is  known  as  anoxyhsemia,  or  want  of  oxygen  in 
the  blood.  Dyspnoea  takes  place  not  only  because  the  air  inspired  con- 
tains oxygen  in  a  given  volume,  but  the  dissolution  of  this  gas  in  the 
blood  is  less  easy  under  feeble  pressure.  Muscular  work  in  the  ascent 
also  uses  up  considerable  of  the  oxygen  taken  in.  At  10  per  cent,  of  an 
atmosphere  there  ensues  restlessness  and  dyspnoea,  and,  at  about  7  per 
cent.,  death.  A  partial  pressure,  like  7  per  cent,  of  an  atmosphere, 
corresponds  to  an  altitude  of  30,000  feet.  Men  in  a  balloon  have 
ascended  about  28,500  feet.  People  who  live  on  high  mountains  have 
a  disease  known  as  the  mal  de  montagne. 

In  mountain  sickness  Kronecker  holds  that  there  is  an  increased 
amount  of  blood  in  the  pulmonary  vessels,  due  to  an  increase  in  their 
capacity  and  to  a  stagnation  of  blood  arising  from  an  equalization  of 
the  atmospheric  and  intrathoracic  pressure,  causing  a  passive  oedema 
resulting  in  dyspnoea  and  asphyxia. 

Ventilation, — Let  it  suffice  here  to  recall  that  the  problem  of 
ventilation  consists  in  maintaining,  in  more  or  less  closed  spaces,  the 
normal  composition  of  the  atmospheric  air.  Not  only  this,  but  to 
counteract  the  incessant  modifications  the  respiration  of  man  or  of  ani- 
mals makes  this  medium  undergo.  For  these  purposes  it  is  important 
that  the  ventilation  should  be  very  active. 

It  has  been  established  that,  for  closed  spaces  intended  to  receive 
healthy  persons,  it  suffices  that  the  ventilation  furnish  1000  cubic  feet 
of  new  air  per  person  per  hour.  This  is  not  sufficient  for  hospitals 
which  contain  sick  persons,  where  more  abundant  and  vitiated  emana- 
tions are  received  by  organisms  less  fitted  to  react  against  their  influ- 
ence. Those  hospitals  which  receive  3000  cubic  feet  of  fresh  air  for 
each  sick  person  hourly  are  free  from  odor. 

A  healthy  adult  gives  off  about  0.6  cubic  feet  of  carbonic  acid  per 
hour.  If  he  be  supplied  with  1000  cubic  feet  of  fresh  air  per  hour  he 
will  add  0.6  to  the  0.4  cubic  feet  of  carbonic  acid  it  already  contains. 
That  is,  he  raises  the  percentage  to  1.0. 


276  PHYSIOLOGY. 

Pharmacological. — The  increase  of  pressure  in  the  pulmonary 
circulation  and  a  simultaneous  decrease  of  arterial  tension  in  the 
systemic  circulation  by  amyl  nitrite  is  due  either  to  a  contraction 
of  the  pulmonary  vessels  or  to  a  weakness  of  the  left  ventricle  and 
as  a  consequence  a  backing  up  of  blood  in  the  left  auricle.  Mtro- 
glycerin  acts  like  nitrite  of  amyl.  Aconite  lowers  the  pressure  in 
both  the  pulmonary  and  systemic  circulations,  due  to  a  weakening  of 
both  sides  of  the  heart.  Ergot  constantly  causes  a  marked  increase 
of  pulmonary  tension  with  a  primary  decrease  of  aortic  pressure. 
Digitalis,  strophanthin,  and  adrenal  extract  increase  the  tension  in 
the  systemic  circulation,  leaving  the  pressure  in  the  pulmonary  circu- 
lation unchanged.  It  is  singular  that  the  adrenal  extract  should 
so  greatly  affect  the  systemic  pressure  and  not  the  pulmonary,  while 
ergot  acts  reversely — augments  the  pulmonary  pressure  more  than 
that  of  the  aortic  system.  These  facts  show  the  independence  of  the 
pulmonary  vessels  to  the  vessels  of  the  systemic  circulation.1 

The  blood-pressure  in  the  pulmonary  artery  is  about  one-third 
that  in  the  aorta. 

As  to  the  vasomotor  nerves  of  the  lungs,  we  do  not  know  if  they 
have  a  tonus,  or  under  what  circumstances  they  are  called  into  activity. 
It  is  natural  to  conclude,  since  pulmonary  vasomotor  nerves  exist,  that 
they  are  excited  when  the  left  heart  has  difficulty  in  emptying  itself; 
in  this  case  they  could  contract  and  diminish  the  afflux  of  blood  to  the 
left  side  of  the  heart. 


Tigerstedt,  "Ergebnisse  der  Physiologie,"  1903. 


CHAPTER  VIII. 

SECRETION. 
INTERNAL  SECRETION. 

THE  tissue-activity  of  the  organism  may  be  conveniently  classed 
under  three  groups :  (a)  muscular  activity,  manifesting  itself  in  heat 
and  motion;  (b)  nervous  activity,  including  all  nervous  acts,  from 
sensation  to  reason ;  (c)  glandular  activity,  which  is  the  general  func- 
tion of  epithelial  and  lymphoid  tissues.  It  includes  all  those  changes 
of  metabolism  whereby  there  follows,  as  a  result  of  elaboration,  a 
special  mixture. 

It  is  with  the  last  of  the  three — glandular  activity — that  we  are 
now  to  deal.  However,  the  human  economy  being  such  a  complex 
organism,  it  must  be  borne  in  mind  that  disturbance  or  lack  of 
activity  of  one  kind  may  have  a  very  marked  influence  upon  other 
metabolic  functions.  It  is  well  known,  especially  among  animal  fan- 
ciers, what  a  great  effect  the  removal  of  the  ovaries  and  testicles  may 
occasion  in  the  development  of  other  organs  and  in  the  general  nutri- 
tion of  the  body.  Proteid  waste  of  increased  proportion  follows  the 
removal  of  a  considerable  portion  of  renal  tissue.  The  liver  is  most 
intimately  connected  with  the  metabolism  of  carbohydrates  and  pro- 
teids  as  well  as  those  food-constituents  which  contain  iron. 

The  gland-cells  perform  an  essential  role  in  secretion.  These 
cells  are  applied  upon  the  basement  membrane  of  the  glandular  acini 
in  such  a  fashion  that  each  cul-de-sac  is  surrounded  by  a  network  of 
capillaries.  Ludwig  and  Tomsa  have  shown  that  between  the  blood- 
capillaries  and  acinus  are  found  lymphatic  spaces.  The  cells  of  the 
acinus,  surrounded  by  the  lymph  in  the  spaces,  take  from  it  the  ele- 
ments needed  for  the  production  of  its  own  peculiar  secretion. 

Dependent  upon  the  nature  of  the  activity  of  the  epithelium  of 
the  glands,  the  general  process  of  secretion  may  be  said  to  comprise 
four  distinct  modes : — 

1.  Secretion  by  Filtration. — In  this  case  the  glandular  epithelium 
does  not  manufacture  any  material;  it  utilizes  the  principles  pre- 
existing in  the  blood  and  lymph.  This  kind  of  secretion  is  related  to 
serous  transudation,  as  of  the  pleurae  and  peritoneum,  but  it  is  not  a 

(277) 


278  PHYSIOLOGY. 

simple  filtration.  The  selective  action  of  the  epithelium  acts  upon  the 
transit  of  the  secretion  and  varies  the  proportion  of  the  constituents 
of  the  secretion  according  to  the  composition  of  the  lymphatic  and 
blood-plasma.  To  this  style  of  secretion  belongs  the  water  of  the 
urine,  sweat,  and 'tears.  The  most  important  principles  filtered  are 
water,  salts  of  the  plasma,  chlorides  of  potassium,  sodium  phosphates, 
lime,  magnesia,  and  carbonic  acid. 

2.  Secretion   Proper  —  Production   of   New   Principles.  —  Here 
glandular  activity  especially  intervenes;    the  epithelial  cell  does  not 
act  as  a  simple  filter.     It  modifies  the  nature  of  those  products  passing 
through  it,  or  creates  from  them  new  products.     In  this  class  may  be 
put  the  digestive  secretion.     The  products  thus  formed  by  gland- 
cells  vary  for  each  gland,  neither  is  physiology  nor  histology  able  to 
explain  their  manner  of  production.     Thus,  we  are  not  able  to. explain 
in  a  satisfactory  manner  the  chemical  changes  which  make  hydro- 
chloric acid  appear  in  the  gastric  juice,  sulphocyanide  of  potassium  in 
the  saliva,  bile-acids  in  the  bile,  etc. 

3.  Secretion  by  Glandular  Desquamation. — In  the  preceding  types 
of  secretion  the  gland-cell  preserves  its  integrity ;   it  does  not  do  any- 
thing else  except  allow  the  external  materials  to  pass  through  it, 
changed  or  unchanged.     However,  in  this  type  the  cell  itself  falls  and 
is  eliminated  to  contribute  to  form  the  product  of  secretion.     This 
glandular  desquamation  is  comparable  to  the  epithelial  desquamation 
which  occurs  during  the  life-history  of  the  epidermis.     Generally  this 
desquamation  is  preceded  by  a  chemical  change  of  the  gland-cells. 
This  change  is  fatty,  as  in  sebaceous  secretion.     The  sebaceous  fats 
and  mucin  form  the  special  products  of  this  group  of  secretions. 

4.  Morphological  Secretion. — In  this  type  the  essential  element 
of  the  secretion  is  a  formed  element.     It  is  a  specialized  cell  derived 
from  a  cell,  together  with  a  liquid  which  holds  this  anatomical  element 
in  suspension.     Such  is  the  spermatic  fluid. 

Secretion  Denned. — The  term  secretion  has  been  defined  as  the 
special  activity  of  the  glandular  tissues.  It  is  the  elaboration  of  fluid 
or  semifluid  mixtures  by  selection  and  formation  from  the  fluids  which 
surround  the  active  cells,  as  well  as  from  the  substances  of  the  cells 
themselves.  Up  to  a  certain  point  secretion  is  composed  of  two  acts 
which  are  separated  by  a  distinct  line  of  demarcation. 

1.  A  filtration  of  blood-plasma  passes  through  the  wall  of  the 
capillary.  This  plasma  spreads  into  the  lymph-spaces  which  surround 
the  acini,  and  it  is  from  this  lymph  that  the  elements  are  taken  out 
for  the  production  of  the  secretory  products.  The  filtration  is  under 


SECRETION.  279 

the  influence  of  the  blood-pressure,  and  varies  in  its  intensity  as  the 
arterial  tension  varies.  It,  properly  speaking,  is  an  accessory  act  of 
secretion. 

2.  The  second  feature  is  the  activity  of  the  gland-cells,  which 
take  from  the  lymph  the  materials  necessary  for  secretion,  to  change 
them  more  or  less.  This  phase  is  the  essential  act  of  secretion.  It  is 
dependent  upon  filtration  to  the  extent  that  filtration  furnishes  the 
liquid  which  the  glandular  cells  need  and  renews  it  when  exhausted. 

The  activity  of  the  gland-cells  attains  its  maximum  in  general 
during  the  apparent  repose  of  the  gland.  When  the  gland  is  not 
secreting,  its  cells  are  preparing  substances  peculiar  to  each  secretion. 
This  is  true  particularly  of  the  ferments,  as  pepsinogen,  trypsin- 
ogen,  etc. 

The  two  processes — filtration  and  gland-cell  activity — may  be 
separated  from  one  another  without  producing  any  interference.  Thus, 
secretion  can  continue  when  the  head  is  amputated  and  even  if  the  cir- 
culation of  the  gland  be  arrested.  Salivation  can  continue  after  both 
these  events  have  occurred. 

On  the  other  hand,  the  injection  of  carbonate  of  soda  into  the 
salivary  duct  destroys  the  gland  activity  without  affecting  the  circula- 
tion of  the  gland.  Should  the  chorda  tympani  be  stimulated  filtra- 
tion from  the  blood  continues,  but  the  gland  does  not  secrete.  There 
is  an  accumulation  of  lymph  in  the  lymph-spaces  until  the  gland 
becomes  cedematous. 

NATURE  OF  INTERNAL  SECRETION. 

This  is  not  the  same  for  all  of  the  glands.  The  secreted  product 
may  be  destined  to  destroy  the  noxious  principles  resulting  from  the 
functions  of  the  organ,  as  of  the  liver  and  suprarenal  capsules.  Its 
aim  may  be  to  break  up  the  excess  of  sugar,  as  is  the  case  with  the 
pancreas ;  or  to  prevent  excess  of  a  colloid  material,  as  with  the  thyroid 
gland.  The  enrichment  of  the  blood  with  useful  principles  is  accom- 
plished by  the  sugar  of  the  liver.  The  testicle  extract  supplies  more 
nervous  energy. 

THE  THYROID. 

The  thyroid  gland,  when  fully  developed,  has  no  excretory  duct; 
so,  with  the  spleen,  suprarenal  bodies,  and  thymus,  it  is  usually  classed 
under  the  head  of  ductless  glands. 

The  thyroid  is  a  soft,  reddish  body  embracing  the  front  and  sides 
of  the  upper  extremity  of  the  trachea.  It  consists  of  a  pair  of  lateral 


280  PHYSIOLOGY. 

lobes  united  at  their  lower  part  by  a  transverse  isthmus.  The  lateral 
lobes  are  oblong  oval,  thicker  below  than  above,  and  usually  of  un- 
equal length.  The  weight  of  the  thyroid  is  usually  from  one  to  two 
ounces,  but  is  larger  in  the  female.  It  is  very  liable  to  become  hyper- 
trophied,  especially  in  the  female :  a  condition  called  goiter. 

The  thyroid  is  a  highly  vascular  organ,  invested  with  a  thin, 
fibrous  membrane,  and  composed  of  a  fibrous  stroma,  in  the  meshes 
of  which  a  multitude  of  minute  closed  vesicles  exist. 

Each  little  lobule  seems  to  be  a  completely  closed  sac — at  least, 
no  tubule  is  noticed  emanating  from  it.  The  little  sacs  are  filled 
with  a  transparent,  amber-colored,  viscid,  nucleo-albuminous  fluid. 
In  the  connective  tissue  surrounding  each  lobule  there  is  a  plexus 
of  capillaries.  With  them  there  is  found  an  abundant  supply  of 
lymphatics. 

Vessels  and  Nerves. — The  arterial  supply  for  the  thyroid  body 
is  gained  from  the  superior  and  inferior  thyroid  arteries.  These  ar- 
teries are  remarkable  for  their  large  size  and  numerous  anastomoses. 
The  veins  form  a  plexus  upon  the  front  of  the  trachea  and  surface  of 
the  gland.  From  the  plexus  arises  the  superior,  middle,  and  inferior 
veins.  The  lymphatics  terminate  in  the  thoracic  and  right  lymphatic 
ducts.  The  nerve-supply  to  the  thyroid  body  is  derived  from  the  mid- 
dle and  inferior  cervical  ganglia  of  the  sympathetic  and  the  pneumo- 
gastric.  Their  nonmedullated  fibers  adhere  very  closely  to  the  vessels. 

Function. — It  was  shown  by  one  observer  that  gentle  pressure 
upon  the  lobes  of  the  gland  caused  the  contents  of  the  gland-acini,  or 
vesicles,  to  flow  into  the  peripheral  lymphatics.  This  was  later  con- 
firmed by  the  work  of  microscopists,  and  the  colloid  nature  of  the 
secretion  was  also  recognized.  The  vesicular  epithelium  is  a  true 
secretory  "gland-tissue  which  separates  the  colloid  material  from  the 
blood.  The  secretory  character  of  the  epithelium  has  been  further 
shown  by  the  injection  of  pilocarpine.  Following  its  administration 
there  results  a  remarkable  increase  in  secretion  of  the  colloid  sub- 
stance. It  has  been  demonstrated  that  the  expressed  juice  of  a  thyroid 
gland  of  a  dog  produced  coma  in  another  animal  three  hours  after 
its  administration. 

Hence  it  must  be  concluded  that  the  thyroid  gland  is  a  structure 
essentially  connected  with  the  metabolism  of  the  blood  and  tissues. 
In  performing  its  functions  it  is  a  blood-agent,  both  directly  and  in- 
directly. In  the  human  fcetus  the  gland-tubes,  or  rather  cylinders  of 
epithelium,  commence  their  secretory  activity  during  the  interval  from 
the  sixth  to  the  eighth  month.  In  proportion  to  the  body-weight,  the 


SECRETION.  281 

gland  is  heaviest  at  birth  and  diminishes  notably  toward  the  end  of 
life.  Therefore  the  thyroid  gland  is  in  functional  activity  before 
birth,  and  is  of  special  metabolic  importance  in  early  extra-uterine 
life.  Its  value  falls  as  the  general  vital  processes  decrease. 

The  thyroid  body  is  one  of  those  organs  of  great  metabolic  im- 
portance, since  its  removal  or  disease  is  followed  by  general  disturb- 
ances. Experimental  thyroidectomy  is  very  much  more  fatal  in  young 
animals  than  in  adults.  The  removal  of  the  gland  in  aged  carnivora 
is  followed  by  the  usualcachexia. 

CACHEXIA  STRUMIPE!IVA  has  been  found  by  all  observers  to  occur 
with  greater  frequency  when  thyroidectomy  has  been  performed  on 
young  individuals. 

The  classification  of  symptoms  from  removal  of  the  thyroid  are 
either  (a)  tetany,  (b)  myxcedema,  and  (c)  cretinism.  According  to 
the  violence  of  the  cachexia,  death  may  occur  in  any  of  these  stages. 

The  nervous  symptoms  appear  early  and  are  well  marked.  The 
first  indication  is  fibrillary  muscular  tremor  or  twitching,  resembling 
very  closely  the  disease  called  tetany ;  next  tremor  occurs ;  and  finally 
rigidity  makes  its  appearance.  Some  experimentalists  hold  that  it  is 
the  removal  of  parathyroids  which  cause  tetany,  and  not  the  removal  of 
the  thyroid. 

When  the  thyroid  body  is  diseased  or  removed  from  children  so 
that  its  functions  are  obliterated,  there  is  produced  a  species  of  idiocy 
called  cretinism. 

A  like  condition  in  adults  receives  the  name  of  myxczdema. 
Noticeable  symptoms  of  this  disease  are  slowness  of  both  body  and 
mind,  associated  with  tremors  and  twitchings.  There  is  also  a  peculiar 
condition  of  the  skin  wherein  there  is  overgrowth  of  the  subcutaneous 
tissue.  In  time  this  becomes  replaced  by  fat.  Myxcedema  was  ba- 
lieved  to  be  an  cedematous  condition  characterized  by  the  presence 
of  a  large  amount  of  mucin.  That  there  is  an  excess  of  mucin  has 
been  determined,  but  it  is  not  in  proportion  to  produce  this  patho- 
logical condition.  The  disease  is  rather  a  hyperplasia  of  the  con- 
nective tissue.  The  integument  especially  swells  and  the  eyelids 
become  puffy.  At  the  same  time  the  surface  becomes  dry  and  there 
is  a  tendency  to  shed  hairs  and  superficial  epithelium.  The  hyper- 
plastic  change  is  followed  by  atrophic  changes,  accompanied  at  first 
by  slight  fever;  later  the  temperature  becomes  subnormal. 

All  of  these  various  effects  of  thyroidectomy  can  be  temporarily 
prevented  by  a  graft  of  thyroid ;  they  may  also  be  caused  to  disappear 
either  by  injection  of  thyroid  juice  into  a  vein  or  under  the  skin.  The 


282  PHYSIOLOGY. 

same  results  may  be  attained  by  raw  thyroid  or  thyroid  juice  by  the 
mouth.  If  a  graft  can  be  made  to  "take,"  the  effects  are  permanent. 
Eemoval  of  a  permanent  graft  will  be  followed  by  all  the  symptoms  of 
thyroidectomy. 

The  phenomena  attending  extirpation  are  due  to  the  absence  of  a 
secretion  which  is  formed  within  the  thyroid,  passing  from  it  into  the 
blood.  This  secretion  is  necessary  for  certain  of  the  metabolic  proc- 
esses of  the  animal  economy,  especially  for  those  connected  with  the 
nutrition  of  the  central  nervous  system  and  connective  tissues.  Ex- 
tracts of  thyroid  gland  produce  distinct  pathological  effects  in  the 
normal  subject.  An  injection  into  a  vein  of  the  decoction  of  the 
gland  lowers  the  blood-pressure  and  increases  the  caliber  of  the  radial 
artery.  From  this  it  would  seem  that  the  juice  has  a  distinct  action 
upon  the  vascular  system. 

Whether  the  gland  possesses  the  function  of  destroying  toxic 
products  of  metabolism  which  would  otherwise  tend  to  accumulate  in 
the  blood  is  a  point  not  as  yet  understood. 

Because  of  the  extreme  vascularity  of  this  organ  and  its  direct 
connection  with  the  vessels  which  supply  blood  to  the  head,  the  thy- 
roid has  been  regarded  as  exercising  a  regulatory  function  on  the 
blood-supply  to  the  brain — short-circuiting  the  cerebral  flow,  as  it  were. 

Experiments  have  showed  that  at  least  a  part  of  the  thyroid  gland 
must  be  allowed  to  remain  after  operations  upon  this  gland.  Other- 
wise cachexia  will  follow. 

The  occurrence  of  thyroid  tissue  in  other  parts  than  the  lobes 
of  the  glands  is  a  matter  of  more  than  embryological  interest.  These 
glandular  masses  have  been  termed  accessory  thyroid  glands,  or  para- 
thyroids. The  parathyroids  lie  in  the  immediate  neighborhood  of 
the  lobes  -of  the  thyroid  gland.  It  has  been  observed,  after  complete 
thyroidectomy  in  man,  that  these  islands,  or  parathyroids,  become 
enlarged.  Also,  where  temporary  symptoms  of  cachexia  have  ap- 
peared, they  improve  in  proportion  to  the  degree  of  swelling  of  the 
parathyroids. 

The  thyroid  contains  two  albuminous  bodies,  the  one  containing 
iodine,  the  other  having  phosphorus.  The  first  one  has  the  character 
of  a  globulin  and  has  received  the  name  of  thyreoglobulin  and  by 
reagents  is  changed  into  iodothyrin. 

Hutchinson  states  that  "if  the  presence  of  iodine  in  iodothyrin 
is  essential  to  the  activity  of  this  substance,  it  is  not  so  in  virtue  of 
its  being  iodine,  but  owing  to  the  form  of  organic  combination  in  which 


SECRETION.  283 

it  occurs/'  It  is  estimated  that  the  normal  thyroid  gland  contains 
approximately  ten  times  as  much  iodine  as  do  the  hypertrophied  glands 
of  patients  suffering  from  exophthalmic  goiter.  The  thyroid  seems  to 
possess  a  peculiar  affinity  for  iodine. 

While  our  knowledge  of  the  thyroid  has  been  considerably  ex- 
tended by  reason  of  modern  research,  there  yet  remains  much  that  is 
very  obscure.  Thus,  the  accessory  thyroid  glands,  or  parathyroids,  are 
free  masses  of  tissue  located  in  the  vicinity  of  the  thyroid  and  which 
seem  to  contain  no  colloid  material.  Nevertheless,  their  removal, 
although  the  bulk  be  small,  produces  identical  results  with  the  com- 
plete removal  of  the  thyroid  gland.  Eegarding  the  function  of  the 
parathyroids,  it  is  probable  that  they  are  concerned  in  removing  some- 
thing from  the  blood  rather  than  adding  anything  to  it. 

Thyroid  by  the  mouth  reduces  weight  by  an  increase  of  the  intake 
of  oxygen  and  the  output  of  carbon  dioxide.  This  excessive  burning 
of  fat  produces  water,  thus  causing  increased  secretion  of  urine.  It 
also  increases  the  urinary  nitrogen,  probably  due  to  proteid  changes. 
It  acts  best  in  the  pale,  fat  person. 

Von  Cyon  has  made  a  study  of  the  relation  of  the  thyroid  to  the 
heart.  He  states  that  suppression  of  the  activity  of  the  thyroid  or 
an  injection  of  iodothyrin  has  an  immense  influence  upon  the  entire 
nervous  system  of  the  heart  and  blood-vessels.  He  proves  that  the 
vagus  participates  in  the  innervation  of  the  thyroid  gland,  or  is  at 
least  closely  connected  with  it.  The  function  of  the  thyroid  is  to 
render  harmless  the  salts  of  iodine,  which  have  a  toxic  effect  upon  the 
vagi  and  sympathetic  nerves  by  converting  them  into  an  organic  com- 
pound, the  iodothyrin.  The  latter  compound  has  a  stimulating  effect 
upon  these  same  nerves  and  at  the  same  time  increases  their  power. 
The  thyroid  acts  mechanically  as  a  safeguard  of  the  brain  against  en- 
gorgement. In  a  sudden  increase  of  blood-pressure,  whether  from 
increased  activity  of  the  heart  or  from  increased  capillary  resistance, 
the  thyroid  is  capable  of  passing  through  its  vessels  a  large  amount 
of  blood  within  a  very  short  time,  so  as  to  turn  it  directly  from  the 
arterial  into  the  venous  system  and  thus  prevent  its  entrance  into 
the  cerebral  circulation. 

THE  SPLEEN. 

The  spleen  is  deeply  placed  in  the  left  hypochrondium.  Its  shape 
is  a  half-ovoid.  Its  consistency  is  comparatively  soft,  and  its  color 
is  purplish.  Its  external  convex  surface  is  in  contact  with  the  dia- 
phragm opposite  the  three  or  four  lower  ribs.  Its  internal  surface  is 


284  PHYSIOLOGY. 

applied  to  the  fnndus  of  the  stomach,  to  which  it  adheres  by  the  gastro- 
splenic  omentum.  In  the  middle  of  the  internal  surface  of  the  spleen 
there  is  a  slight  groove,  the  hilus,  where  the  artery  and  nerves  enter. 
The  spleen  usually  is  five  inches  in  length,  four  inches  in  breadth,  and 
from  one  to  one  and  one-half  inches  thick.  It  has  two  coats:  the 
outer  serous  and  the  inner  fibro-elastic. 

The  spleen  when  torn  has  a  deep  reddish-black,  pulpy  appearance, 
resembling  coagulated  blood.  This  splenic  pulp  may  be  removed  from 
the  spleen  by  maceration,  leaving  a  spongy  mass  composed  of  splenic 
blood-vessels  associated  with  numerous  trabeculaB  of  fibro-elastic  tissue. 
Adhering  to  the  side  of  the  smallest  arteries  of  the  spleen  are  small, 
rounded,  whitish  bodies,  the  corpuscles  of  Malpighi,  one-thirtieth  to 
one-sixtieth  of  an  inch  in  diameter.  The  splenic  pulp  contains  red 
blood-corpuscles,  granular  corpuscles  resembling  lymphocytes  in  ap- 
pearance and  having  an  amoeboid  movement,  and  red  corpuscles  under- 
going disintegration. 

Function. — The  extirpation  of  the  spleen  leaves  life  and  health 
intact  in  animals  and  in  man.  All  that  results  is  a  more  or  less 


Fig.  62. — Tracing  of  an  Experiment  with  Splenic  Extract  upon  a  Dog. 
Read  from  left  to  right. 

pronounced  hypertrophy  in  all  the  lymphatic  ganglia  of  the  body. 
Direct  irritation  of  the  spleen,  the  direct  or  reflex  irritation  of  the 
medulla  oblongata,  the  application  of  ice-water  to  the  left  hypo- 
gastrium,  and  quinine  cause  a  diminution  of  the  spleen  by  contraction 
of  the  muscles  of  the  capsule  and  trabecula.  The  spleen  is  congested 
during  digestion,  and  when  the  portal  circulation  is  interfered  with, 
and  in  a  great  number  of  infectious  diseases,  notably  typhoid  and 
malarial  fevers.  The  spleen  is  supposed  by  some  to  manufacture  white 
blood-corpuscles,  and  this  manufacturing  reaches  a  pronounced  activ- 
ity when  the  organ  is  hypertrophied,  as  in  Ieucocytha3mia.  The  spleen, 
from  its  power  to  dilate,  serves  as  a  reservoir  of  blood  for  the  portal 
system,  especially  for  the  blood-vessels  of  the  stomach.  Many  of  the 
purin  bodies  are  found  in  the  spleen,  as  xanthin,  hypoxanthin,  and 
uric  acid. 

Influence  of  the  Nervous  System  Upon  the  Spleen. — The  nerves 
that  supply  the  spleen  have  their  center  in  the  medulla  oblongata. 
Section  of  these  nerves  is  followed  by  an  increase  in  the  size  of  the 
organ. 


SECRETION.  285 

It  has  been  shown  by  the  oncometer  that  the  spleen  undergoes 
rhythmical  contractions  and  dilatations  by  virtue  of  the  regular  con- 
traction and  relaxation  of  the  muscular  fibers  found  in  its  capsule  and 
trabecula?. 

I  have  demonstrated  experimentally  that  extract  made  from  the 
spleen  when  injected  into  an  animal  will  excite  active  peristaltic  move- 
ments (Fig.  62). 

THE  ADRENALS. 

The  adrenals  are  a  pair  of  flattened  triangular  organs,  one  being 
situated  upon  the  upper  end  of  each  kidney  and  inclined  inwardly 
toward  the  vertebral  column.  Their  posterior  surface,  moderately 
convex,  rests  against  the  crura  of  the  diaphragm;  their  anterior  sur- 
face, flatter  than  the  posterior,  on  the  right  side  is  in  contact  with  the 
liver,  on  the  left  side  with  the  pancreas  and  spleen.  The  surfaces 
present  vascular  furrows,  the  largest  of  which  at  the  base  is  dis- 
tinguished as  the  hilus.  These  adrenals  are  in  color  brownish  yellow, 
of  moderately  firm  consistence,  and  vary  in  size  in  different  individuals 
and  slightly  on  the  two  sides.  Usually  they  are  about  one  and  one-half 
inches  in  breadth  and  height,  and  about  one-fourth  of  an  inch  in 
thickness.  On  section  we  find  an  external  layer,  the  cortex,  and  an 
internal  layer  of  softer  substance,  the  medulla. 

The  cortical  layer  is  yellow  in  color,  of  firm  consistence,  and  pre- 
sents a  columnar  appearance  at  right  angles  to  the  surfaces  of  the 
layer.  Microscopically,  it  contains  oblong  receptacles  occupying  a 
fibrous  stroma  continuous  with  the  fibrous  coat  of  the  body.  In 
these  receptacles  are  nucleated,  transparent  cells  often  containing  oil- 
globules  and  a  yellowish-brown  pigment.  Beneath  the  capsule  is  the 
zona  glomerulosa,  with  cells  in  round  groups;  the  next  is  the  zona 
fasciculata,  with  cells  in  columns;  and  the  last  the  zona  reticularis. 

The  medullary  substance  is  composed  of  very  irregularly  shaped 
cells,  rather  closely,  but  irregularly,  packed  into  a  meshwork  of  fibrous 
tissue.  In  the  interstices  lie  masses  of  multinucleated  protoplasm, 
blood-vessels,  and  an  abundance  of  nerve-  fibers  and  cells. 

The  cells  of  the  medulla  are  conspicuous  in  that  they  contain 
certain  reducing  agents.  The  agent  which  gives  color-reactions  has 
been  termed  chromogen.  Just  what  this  agent  is  chemically  is  not 
known,  but  it  is  believed  to  be  the  principle  which  raises  blood-pressure 
when  suprarenal  extracts  are  injected  subcutaneously.  The  active 
principle  is,  according  to  Abel,  epinephrin;  according  to  Takamine, 
adrenalin. 


286 


PHYSIOLOGY. 


Blood-supply. — The  blood-vessels  of  these  suprarenal  bodies  are 
numerous.  Each  is  supplied  by  the  suprarenal  artery  from  the  aorta, 
together  with  branches  from  the  contiguous  phrenic  and  renal  arteries. 
When  the  arteries  enter  the  organ  they  ramify  through  the  fibrous 
stroma  and  terminate  in  capillaries  surrounding  the  receptacles  of  the 
granular  cell-contents.  The  nerves  are  chiefly  derived  from  the  solar 
and  renal  plexuses  of  the  sympathetic  system,  and  are  very  numerous 
for  the  size  of  the  organ. 

Function.  —  The  function  of  the  suprarenal  bodies  is  still  very 
obscure.  The  discovery  that  a  relation  existed  between  the  bronzing 
of  the  skin  of  Addison's  disease  and  a  diseased  condition  of  the  supra- 
renals  was  a  signal-point.  It  was  learned  that  these  small  bodies  are 
indispensable  to  life.  The  phenomena  ensuing  from  their  extirpa- 
tion are  due  to  a  chemical  alteration  of  the  blood,  and  not  to  trauma. 


Fig.  63. — I.  Dog.    Arrest  of  Peristalsis  by  30  Drops  of  Adrenalin.    II.  Dog, 
Arrest  of  Peristalsis  for  a  Minute  and  a  Half  by  20  Drops 

of  Adrenalin  Solution. 
Read  from  left  to  right.     The  minute  curves  are  cardiac  pulsations. 

The  ablation  of  one  capsule  is  not  necessarily  mortal,  but  the  destruc- 
tion, of  both  produces  death  very  quickly.  In  the  rabbit  death  follows 
in  nine  hours;  in  th'e  guinea-pig,  in  three  hours.  Death  is  preceded 
by  a  considerable  weakness,  true  paralysis  of  the  members  and  respira- 
tory muscles,  and  epileptiform  convulsions. 

If  the  blood  of  animals  dying  from  removal  of  the  capsules  be 
transfused  into  an  animal  that  has  just  undergone  the  operation,  there 
is  produced  a  very  rapid  paralysis  and  death.  Injecting  an  extract  of 
the  capsules  into  an  animal  from  whom  the  capsules  have  been  removed 
slowed  the  symptoms  and  prolonged  life.  Hence,  it  has  been  con- 
cluded that  the  chief  function  of  the  suprarenal  capsules  is  the  neu- 
tralization of  a  poison  analogous  to  curare.  The  means  by  which  this 
is  accomplished  is  a  poison-destroying  secretion  in  their  cells.  The 
poison  to  be  neutralized  is  manufactured  in  the  organism  and  accumu- 
lates in  the  blood  in  instances  of  lesion  or  removal  of  the  suprarenals. 


SECRETION.  287 

I  have  shown  that  adrenalin,  the  active  principle,  arrests  peri- 
stalsis in  diastole.  This  has  been  confirmed  by  Prof.  Pal,  of  Vienna. 
Dr.  Pal  believes  that  the  arrest  of  the  intestinal  peristalsis  is  due  to 
vasoconstriction  by  the  adrenals,  while  the  after-increase  of  peristalsis 
is  caused  by  a  return  of  a  full  irrigation  by  the  blood.  We  have,  then, 
two  glands,  one  of  which  arrests  peristalsis — the  adrenal ;  the  other, 
which  excites  it — the  spleen.  Blum  has  shown  that  adrenalin  causes 
glycosuria. 

Oliver  and  Schafer  found  that  when  extracts  of  the  suprarenals 
were  injected  into  the  circulation  very  noticeable  phenomena  resulted. 
Thus,  the  arteries  become  greatly  contracted,  the  blood-pressure  rises 
very  rapidly,  and  the  action  of  the  heart  is  greatly  augmented.  This 
vasoconstrictor  action  is  independent  of  the  main  vasomotor  center, 
which  I  have  confirmed.  These  two  observers  conclude  that  the  cap- 
sules secrete  a  substance  to  maintain  the  tonicity  of  the  muscular  tis- 
sues in  general  and  the  heart  and  arteries  in  particular. 

Nearly  all  the  adrenalin  is  destroyed  in  the  body,  but  I  have 
shown  that  a  minute  quantity  is  excreted  by  the  kidneys.  One  one- 
millionth  of  a  gram  of  the  dried  gland  will  elevate  the  arterial  tension. 

The  splanchnics  are  supposed  to  contain  the  secretory  nerves  of 
the  adrenals. 

THE  THYMUS. 

The  thymus  body  is  a  temporary  organ  which  increases  in  size 
from  the  embryo  up  to  two  years  after  birth,  and  subsequently  dwindles 
away.  It  occupies  the  upper  part  of  the  anterior  mediastinal  cavity 
behind  the  sternum  and  extends  into  the  neck  frequently  to  the  thyroid 
gland.  It  rests  upon  the  pericardium,  aorta,  and  the  trachea.  It 
is  a  flat,  triangular  body,  consisting  of  a  pair  of  lateral  and  unequal 
lobes.  It  is  of  a  pinkish-cream  color,  and  varies  in  size  and  weight 
not  only  according  to  age,  but  also  in  different  persons.  At  birth  it  is 
about  two  inches  long  and  one  and  one-half  inches  wide  at  the  lower 
part  and  two  to  three  lines  thick.  It  is  composed  of  numerous  angular 
lobules  mixed  with  connective  tissue.  The  lobules  are  subdivided  into 
follicles,  and  each  follicle  has  a  cortex  and  medulla.  In  the  medulla 
are  spherelike  bodies  known  as  the  concentric  corpuscles  of  Hassall. 

Chemical  Composition.  —  The  thymus  is  principally  a  lymph- 
gland.  Nothing  special  is  known  of  the  concentric  corpuscles.  The 
presence  of  extractives,  like  xanthin,  hypoxanthin,  leucin,  and  adenin 
has  been  noted.  The  alkaline  reaction  of  life  becomes  rapidly  acid 
after  death.  The  acid  is  sarco-lactic  acid. 


288  PHYSIOLOGY. 

The  main  constituent  of  the  cells  is  proteid,  especially  nucleo- 
proteid.  The  total  percentage  in  the  thymus  gland  is  about  12.29 
per  cent.  When  it  is  desired  to  produce  experimental  hitravascular 
clotting,  the  thymus  is  usually  employed  as  the  source  for  the  nucleo- 
proteid.  This  property  is  not  characteristic  of  the  thymus,  for  it  is 
found  in  all  protoplasm. 

Function. — Extirpation  gives  few  positive  results,  but  chemical 
investigation  shows  that  the  parenchyma  of  the  gland  contains  a  large 
number  of  products  that  indicate  that  it  possesses  very  considerable 
metabolic  activity.  As  long  as  the  thymus  gland  exists,  it  seems  to 
take  part  in  the  production  of  white  corpuscles  like  other  varieties  of 
lymphatic  tissue.  Some  authors  claim  for  it  the  production  of  red 
corpuscles  in  early  life. 

Extracts  of  the  thymus,  when  injected  subcutaneously,  have  been 
shown  by  Ott  to  increase  the  pulse-rate,  with  a  momentary  rise  of 
pressure,  followed  by  a  fall.  This  has  been  confirmed  by  Svehla  and 
Swale  Vincent.  Svehla  found  that  extirpation  of  the  thymus  of  the 
frog  kills  it.  Swale  Vincent,  however,  did  not  find  that  removal  of 
the  gland  of  the  frog  was  necessarily  fatal,  as  his  frogs  lived  thirty- 
six  days  after  the  operation.  According  to  Vincent,  extirpation  of  the 
gland  of  guinea-pigs  did  not  affect  the  animal  in  any  way. 

PITUITARY  BODY. 

The  pituitary  body  (hypophysis  cerebri)  is  a  small,  reddish-gray, 
vascular  mass,  weighing  from  five  to  ten  grains.  It  is  oval  in  shape, 
situated  in  the  pituitary  fossa  of  the  sphenoid  bone,  and  is  connected 
with  the  end  of  the  infundibulum.  The  body  is  retained  in  position 
by  a  process  of  dura  mater  derived  from  the  inner  wall  of  the  cav- 
ernous sinus. 

Structure. — This  little  pituitary  body  is  very  vascular,  and  con- 
sists of  two  lobes,  separated  from  one  another  by  a  fibrous  stroma. 
The  two  lobes  differ  both  in  development  and  structure. 

The  anterior  lobe  is  of  a  dark  yellowish-gray  color  and  resembles 
in  microscopical  structure  the  thyroid  body  and  suprarenal  bodies.  A 
canal  passes  through  the  anterior  lobe  to  connect  it  with  the  infun- 
dibulum. 

The  posterior  lobe  is  entirely  different  in  that  it  is  developed 
from  an  outgrowth  from  the  embryonic  brain,  and  therefore  is  nervous 
in  its  structure. 

Ablation  of  this  body  in  the  cat  produces  death  in  about  two 
weeks.  The  symptoms  resemble  very  much  those  that  follow  thy- 


SECRETION.  289 

roiclectomy.  Extracts  of  the  infundibular  part  elevate  the  arterial 
tension  by  a  constriction  of  the  arteries  and  slow  the  heart.  This 
substance  is  not  soluble  in  alcohol.  From  a  saline  decoction  of  the 
gland  there  was  obtained  an  alcoholic  precipitate  which  produced  a 
fall  of  arterial  tension;  so  that  there  seems  to  be  two  substances  in 
this  gland  antagonizing  each  other  as  regards  arterial  tension.  Dis- 
ease of  this  gland  produces  the  condition  known  as  acromegaly,  in 
which  the  bones  of  the  face  and  limbs  become  hypertrophied.  It  is 
also  connected  with  giantism. 

EXTERNAL   SECRETION. 

THE  MAMMARY  GLANDS. 

The  mamma?,  or  breasts,  are  accessory  organs  of  the  generative 
system.  They  secrete  the  milk.  They  exist  in  the  male  as  well  as  in 
the  female,  but  only  in  a  rudimentary  condition  in  the  former.  In  the 
female  they  are  two  large,  hemispherical  eminences  situated  toward 
the  lateral  aspect  of  the  pectoral  region.  They  range  between  the  third 
and  seventh  ribs.  Before  puberty  they  are  of  small  size,  but  enlarge 
as  the  generative  organs  become  more  fully  developed.  They  enlarge 
during  pregnancy,  especially  after  delivery.  In  old  age  they  become 
atrophied. 

The  outer  surface  of  the  mammae  is  convex,  with  just  below  the 
center  a  small,  conical  eminence:  the  nipple.  The  surface  of  the 
nipple  is  dark-colored,  and  surrounded  by  an  areola  of  a  colored  tint. 
In  the  virgin  the  areola  is  of  a  delicate,  rosy  hue;  about  the  second 
month  after  impregnation  it  enlarges  and  also  acquires  a  darker  shade 
of  color.  The  color  deepens  as  pregnancy  advances;  in  some  cases  it 
becomes  dark  brown  or  even  black.  After  cessation  of  lactation  there 
is  a  diminution  in  the  quantity  of  pigment,  but  the  original  hue  is 
never  regained.  Change  in  the  color  of  the  areola  is  of  importance 
in  determining  an  opinion  in  cases  of  suspected  first  pregnancy. 

The  nipple  is  a  conical  eminence  that  is  capable  of  erection  from 
mechanical  excitement.  This  is  .mainly  produced  by  the  contraction 
of  its  unstriped,  muscular  tissue,  aided  by  its  numerous  blood-vessels. 
All  tend  to  give  it  an  erectile  structure.  The  nipple  is  perforated  by 
numerous  orifices :  the  apertures  of  the  lactiferous  ducts.  On  its  sur- 
face are  very  sensitive  papillae.  Near  the  base  of  the  nipple  and  upon 
the  surface  of  the  areola  are  numerous  sebaceous  glands.  These  be- 
come enlarged  during  lactation,  their  fatty  secretion  serving  as  a  means 
of  protection  during  the  act  of  sucking. 

i* 


*290  PHYSIOLOGY. 

The  nipple  is  made  up  of  areolar  tissue  interspersed  with 
numerous  blood-vessels  and  plain  muscular  fibers.  The  fibers  are 
arranged  chiefly  in  a  circular  manner  around  the  base,  some 
fibers,  however,  radiating  from  the  base  to  the  apex. 

Structure  of  the  Mammae. — The  mammae  consist  of  gland-tissue. 
Like  other  glands,  they  are  composed  of  large  divisions,  or  lobes,  which 
in  turn  are  subdivided  into  lobules.  The  lobules  and  lobes  are  held 
together  by  means  of  fibrous  tissue,  while  between  the  lobes  are  septa. 

The  mammary  gland-tissue,  in  general,  when  free  from  fibrous 
tissue  and  fat,  is  of  a  pale-reddish  color,  firm  in  texture,  and  circular 
in  form.  The  smallest  lobules  consist  of  a  cluster  of  rounded  vesicles, 
which  open  into  the  smallest  branches  of  the  lactiferous  ducts.  These 
small  ducts  unite  to  form  larger  ducts,  which  later  terminate  in  a 
single  canal.  This  latter  corresponds  with  one  of  the  chief  sub- 
divisions of  the  gland. 

These  main  excretory  ducts,  about  fifteen  or  twenty  in  number, 
are  termed  tubuli  lactiferi.  These  present  in  their  course  a  general 
convergence  toward  the  areola,  beneath  which  they  form  dilata- 
tions: ampullae.  These  dilatations  serve  as  small  reservoirs  for  the 
milk.  During  active  secretion  by  the  gland  the  milk  collecting  in  them 
distends  them.  Each  lactiferous  duct  is  of  an  average  diameter  of 
one  seventy-fifth  of  an  inch,  expanding  into  the  ampulla,  whose  average 
caliber  is  one-fourth  of  an  inch.  At  the  base  of  the  nipple  the  am- 
pullae become  contracted  again  to  pursue  a  straight  course  to  its  sum- 
mit. Each  duct  pierces  the  nipple  by  a  separate  orifice,  whose  opening 
is  about  one-fiftieth  of  an  inch.  The  ducts  are  composed  of  areolar 
tissue  with  elastic  fibers  and  longitudinal  muscular  fibers.  Their 
mucous  lining  is  continuous  at  the  point  of  the  nipple  with  the  integu- 
ment. They  are  lined  internally  by  short  columnar,  and,  near  the 
nipple,  by  flattened  epithelium. 

With  the  exception  of  the  nipple,  the  general  surface  of  the 
mamma  is  covered  with  fat.  The  latter  is  lobulated  by  sheaths  and 
processes  of  connective  tissue,  which  bind  the  skin  and  the  gland 
together  loosely.  It  is  by  this  same  manner  that  the  gland  is  fastened 
to  the  great  pectoral  muscle  beneath  it. 

Blood-vessels,  nerves,  and  lymphatics  are  plentifully  supplied  to 
the  mammary  glands. 

The  arteries  are  derived  from  the  thoracic  branches  of  the  axillary, 
the  intercostals,  and  internal  mammary.  The  veins  describe,  by  their 
frequent  anastomoses,  a  circle  around  the  base  of  the  nipple.  This 
has  been  called  by  Haller  the  circulus  venosus.  From  this  branches 


SECRETION. 


291 


run  to  the  circumference  of  the  gland.  The  caliber  of  the  contained 
vessels,  as  well  as  the  size  of  the  glands,  may  be  increased  during  preg- 
nancy and  lactation.  The  lymphatics  principally  run  along  the  lower 
border  of  the  pectoralis  major  muscle  to  the  axillary  glands.  The 
nerves  are  derived  from  the  supraclavicular  and  the  intercostals.  No 
secretory  nerves  of  the  mammae  exist. 

Each  gland-acinus,  or  vesicle,  consists  of  a  membrana  propria, 
surrounded  externally  with  a  network  of  branched  connective-tissue 
corpuscles.  Internally  there  is  a  somewhat  flattened  polyhedral  layer 
of  nucleated  secretory  cells.  The  size  of  the  lumen  of  the  acini  de- 
pends upon  the  secretory  activity  of  the  glands;  when  it  is  large  the 
vesicle  is  filled  with  milk  containing  numerous  refractive,  fatty 
granules. 


Fig.  64. — Dog's  Mammary  Gland  in  First  Stage  of  Secretion. 
(  HEIDENHAIN.  ) 

a,  6,  Section  through  the  center  of  two  alveoli  of  the  mammary  gland,  the 
epithelial  cells  seen  in  profile.,    c,  Surface  view  of  the  epithelial  cells. 

In  the  gland  of  a  woman  who  is  not  pregnant  or  suckling  the 
alveoli  are  very  small  and  solid.  They  are  filled  with  a  mass  of 
granular,  polyhedral  cells.  During  pregnancy  the  alveoli  enlarge 
while  the  cells  undergo  rapid  multiplication.  With  the  beginning  of 
lactation  the  cells  in  the  center  of  the  alveolus  undergo  fatty  degenera- 
tion and  are  eliminated  in  the  first  milk  as  colostrum-corpuscles.  The 
lining  cells  of  the  alveolus  remain  to  form  a  single  layer  of  granular, 
short,  columnar  cells.  Each  possesses  a  spherical  nucleus,  and  is  at- 
tached to  the  limiting  membrana  propria.  By  means  of  metabolic 
processes  within  the  protoplasm  of  the  cells  the  fats,  salts,  milk-sugar, 
etc.,  are  formed.  During  glandular  activity,  instead  of  one,  two  or 
more  nuclei  are  seen;  the  well-formed  one  is  near  the  base,  the  other 
nearer  the  free  end  of  the  cell.  Near  the  border  of  the  cell  are  seen 
numerous  oil-globules  and  granules.  Some  of  the  larger  oil-globules 
are  seen  projecting  from  the  surface  of  the  cell  as  if  about  to  be  ex- 
truded from  it. 


292  PHYSIOLOGY. 

In  addition  to  this,  a  division  of  the  cell  itself  takes  place:  a 
parting  of  the  cell-substance  with  a  nucleus  in  it.  The  daughter-cell 
thus  cast  off  passes  into  the  alveolus  to  form  a  part  of  the  milk.  The 
secretion  of  milk  is  an  example  of  a  secretion  that  is  eminently  the 
result  of  the  metabolic  activity  of  the  secreting  cell.  The  blood  is 
the  original  source  of  the  milk,  but  it  becomes  milk  only  by  the  action 
of  the  cells  of  the  mammary  gland :  a  metabolism  of  those  cells. 

Ottolenghi  has  found  in  the  active  mammary  gland  of  guinea- 
pigs  the  presence  of  "  Ninsen's  globules,"  which  are  due  to  two  causes : 
first,  an  increase  of  the  nuclei  of  the  epithelium  of  the  gland;  and 
second,  an  infiltration  of  the  gland-cells  with  leucocytes.  This  theory 
is  opposed  to  that  of  Heidenhain,  and  makes  the  milk  secretion  chiefly 
a  disintegration  of  the  nuclei  of  the  epithelium  of  the  gland  rather 
than  a  breaking  up  of  the  protoplasm. 


Fig.  65. — Mammary  Gland  of  the  Dog,  Second  Stage  of  Secretion, 
t  (HE.IDENHAIN.) 

Ottolenghi  also  saw  in  the  milk-glands,  with  islands  of  active 
gland-tissue,  other  islands  of  a  colostrum  type — a  type  of  relative  rest. 

Colostrum. — At  the  beginning  of  the  period  of  lactation  milk  has 
peculiar  characters  and  has  received  the  name  of  colostrum.  This 
term  is  applied  to  the  milk  appearing  during  the  first  week  after 
delivery.  Colostrum  is  acid,  possesses  a  yellow  color,  which  becom.es 
white  toward  the  fourth  day.  It  is  viscid  and  has  a  mean  density  of 
1.056.  It  contains,  in  addition  to  the  fat-globules,  colostrum-corpus- 
cles. These  are  degenerating  polyhedral  cells  which  filled  the  vesicles 
previous  to  lactation. 

I  have  found  that  infusion  of  dried  mammary  gland  decreases 
the  pulse  and  .increases  arterial  tension.  The  blood-pressure  rises 
after  removal  of  the  main  vasomotor  center. 

Functional  Variations  in  Milk. — A  substantial  amount  of  nour- 
ishment augments  the  quantity  of  milk.  Drinks  have  the  same  effect. 
An  exclusive  meat  diet  augments  the  proportion  of  fat  in  the  milk; 
a  small  meat  allowance  in  a  mixed  diet  increases  casein  and  diminishes 


SECRETION.  293 

the  sugar.  A  vegetable  diet  diminishes  the  total  quantity,  lowers  the 
amount  of  casein  and  butter,  but  augments  the  proportion  of  sugar  of 
milk.  A  diet  rich  in  fats  does  not  augment  the  quantity  of  butter,  but 
if  kept  up  too  long  it  diminishes  it.  Atropine  dries  up  the  milk 
secretion;  antipyrin  is  said  to  have  a  similar  effect.  Jaborandi  in- 
creases it.  Alcohol,  frequently  given  in  the  shape  of  porter,  increases 
the  secretion  of  milk. 

THE  SWEAT=GLANDS. 

The  sweat-glands  are  the  organs  which  furnish  the  means  for  the 
elimination  of  a  large  portion  of  the  aqueous  and  gaseous  materials 
excreted  by  the  skin.  They  are  found  in  almost  every  part  of  the 
integument,  being  particularly  numerous  where  hairs  are  absent,  as 
upon  the  palms  and  soles.  Krause  found  the  smallest  number  of 
them  (400  for  each  square  inch)  upon  the  back  and  buttocks;  the 
greatest  number  (2800  per  square  inch)  on  the  surface  of  the  palm  of 
the  hand  and  the  sole  of  the  foot.  By  this  observer  it  was  calculated 
that  the  total  number  of  them  is  2,400,000.  These  glands  may  be- 
come hypertrophic  (in  elephantiasis),  thereby  producing  sudoriparous 
tumors  upon  the  cheek.  Atrophy  also  occurs. 

In  structure  the  sweat-glands  are  small,  lobular,  reddish  bodies. 
Each  one  consists  of  a  single,  convoluted  tube,  from  which  mass  the 
efferent  duct  proceeds  upward  through  the  corium  and  cuticle.  It  is 
somewhat  dilated  at  its  extremity  and  opens  upon  the  surface  of  the 
cuticle  by  an  oblique  valvelike  aperture.  The  efferent  part  of  the  duct 
in  its  course  through  the  skin  presents  a  corkscrew  arrangement  in 
those  places  where  the  epidermis  is  thick. 

The  convoluted  or  coiled  portion  of  the  tube  is  the  place  where 
secretion  takes  place,  and  is  usually  known  as  the  secretory  part  of  the 
sweat-apparatus.  Here  the  tube  is  lined  by  a  single  layer  of  clear, 
nucleated,  cylindrical  epithelium.  Smooth  muscular  fibers  are  ar- 
ranged longitudinally  along  the  tube  in  the  larger  glands.  Beyond 
the  muscular  coat  is  the  basement-membrane;  so  that  the  duct  has  a 
definite  outline  and  exists  as  an  entity  that  is  distinct  from  the  sur- 
rounding tissues. 

The  distal  portion  of  the  tube  serves  the  simple  purpose  of  a 
conduit  for  the  passage  of  the  sweat-secretion  to  the  skin  surface.  It 
contains  no  muscular  fibers  or  basement-membrane.  There  is,  how- 
ever, a  distinct  lumen  surrounded  by  several  layers  of  cubical  cells ;  so 
that  by  some  authorities  this  portion  of  the  apparatus  is  considered  to 
be  but  an  opening  between  epidermal  cells. 


294  PHYSIOLOGY. 

Glands  which  are  constantly  active,,  as  are  the  sweat-glands,  must 
necessarily  require  a  very  liberal  blood-supply.  Each  coil  (the  real 
seat  of  secretion)  is  surrounded  by  a  network  of  capillaries,  whose 
arrangement  is  such  that  the  secretory  cells  are  easily  enabled  to  ob- 
tain the  watery  secretion  from  the  blood-stream. 

Nerves. — A  plentiful  supply  of  nerve-fibers  in  the  form  of  a 
nerve-plexus  ends  in  the  glandular  substance.  That  the  secretion  of 
sweat  is  not  a  mere  filtration  that  varies  according  to  the  blood- 
pressure,  but  a  process  dependent  upon  a  direct  action  of  the  nerve 
upon  the  gland-cell  has  been  demonstrated  by  Ott.  In  experiments 
upon  cats  certain  changes  were  produced  in  the  cell-protoplasm  by 
changes  in  the  activity  of  the  nerve. 

In  the  cat  the  sciatic  was  cut  and  the  animal  kept  until  the 
fifth  day.  At  this  time  the  pads  of  the  feet  were  excised,  placed  in 
absolute  alcohol,  and  when  hard  enough  were  cut  into  sections,  stained 
with  carmine  solution,  and  mounted  in  glycerin. 

In  another  cat  the  sciatic  was  exposed  and  the  nerve  feebly  irri- 
tated for  a  period  of  two  and  one-half  hours,  when  the  pads  of  the 
feet  were  treated  in  the  same  manner. 

Sections  of  the  pads  of  the  feet  of  each  cat  were  then  examined 
microscopically.  It  was  found  that  the  irritated  cells  were  smaller 
than  the  resting  cells,  that  their  protoplasmic  contents  were  more 
granular  and  more  highly  tinged  with  carmine  solution,  although  left 
in  it  the  same  length  of  time  as  the  resting  cell.  These  facts  have 
been  confirmed  by  Eenaut  in  the  horse's  glands. 

Sweat  is  the  secretory  product  of  the  sudoriferous  glands.  It  is 
discharged  in  a  continuous  fashion  upon  the  surface  of  the  skin,  there 
to  be  gotten  rid  of  as  vapor.  As  long  as  the  secretion  is  small  in 
amount  it  is  evaporated  from  the  surface  at  once.  Because  of  this 
feature  it  is  termed  insensible  perspiration.  The  skin  is  supple,  fresh, 
and  without  any  appreciable  humidity. 

When,  however,  the  secretion  of  the  glands  is  increased  in  quan- 
tity or  its  evaporation  arrested,  drops  appear  upon  the  skin.  These 
drops  of  water  form  what  is  commonly  known  as  sweat.  During  this 
condition  the  skin  is  also  supple  and  soft,  but  is  humid.  There  often 
is,  in  fact,  a  visible  liquid. 

Sweat  is  a  more  or  less  transparent  liquid,,  of  a  salty  flavor.  It 
is  constantly  acid  in  reaction  and  has  a  specific  gravity  of  1.004. 

The  acidity  of  the  sweat  is  due  to  acid  sodium  phosphate.  From 
its  being  very  readily  contaminated  it  is  impossible  to  obtain  sweat 
in  a  pure  state. 


SECRETION. 


295 


Fig.  I. 


Fig.  2. 


Ffy.3. 


Fig.  66.— Section  of  Sweat-glands  of  Cat. 

1,  Section  of  gland  five  days  after  section  of  sciatic  nerve.     2,  Gland  with 
sciatic  irritated  two  and  a  half  hours.    3,  Sweat-gland  in  normal  condition. 


296  PHYSIOLOGY. 

The  relation  of  the  sensible  and  insensible  perspirations  varies 
considerably  with  the  temperature  of  the  air.  In  round  numbers,  the 
total  amount  of  sweat  secreted  by  a  man  is  two  pounds  in  twenty- 
four  hours. 

The  quantity  of  solid  components  of  sweat  is,  on  the  average,  1.0 
per  cent.  It  may  descend  to  0.8  per  cent,  when  there  is  an  increase 
in  the  rapidity  of  the  secretion.  That  means  that  in  profuse  perspira- 
tion it  is  the  water  which  acquires  the  predominance.  However,  no 
matter  what  the  celerity  of  the  perspiration,  there  is  a  minimum  of 
solid  components:  0.8  per  cent.  This  remains  unchanged,  showing 
that  the  sweat  is  a  primitive  secretion  in  character. 

Sweat  contains  many  and  different  members  of  the  series  of  fat 
acids,  neutral  fats,  alkaline  sulphates  and  phosphates,  lactic  acid,  and 
urea.  Horse's  sweat  contains  albumin. 

The  different  strength  and  odor  peculiar  to  the  sweat  of  different 
animals  is  due  to  the  variety  and  abundance  of  the  volatile  fatty  acids. 
Of  these,  acetic,  formic,  and  butyric  prevail  in  general,  with  capronic 
and  caprillic.  To  their  prevalence  in  the  armpits  and  feet  is  due  the 
corresponding  intensity  of  odor. 

It  has  been  calculated  that  about  0.08  per  cent,  of  the  sweat  is 
urea.  It  may  be  increased  greatly  in  cholera,  by  reason  of  its  sup- 
pressed passage  through  the  kidneys.  There  is  often  observed  a  crys- 
talline deposit  of  this  substance  upon  the  surface  of  the  body  in  death 
by  cholera. 

Carbonic  acid  and  traces  of  nitrogen  are  found  diffused  in  the 
sweat  and  so  eliminated  from  the  organism. 

Perspiration  is  especially  favored  by  the  elevation  of  the  body- 
temperature  ;  by  the  wateriness  of  the  blood ;  by  the  energetic  action 
of  the  vessels  of  the  heart;  by  increase  of  pressure  in  the  cutaneous 
vessels,  as  during  muscular  exercise,  etc. 

Drugs. — Certain  drugs  favor  sweating.  Such  are  pilocarpine, 
Calabar  bean,  strychnine,  picrotoxine,  muscarine,  nicotine,  camphor, 
and  the  ammonias.  Atropine,  and  morphine  in  large  doses,  diminish 
the  secretion.  I  have  found  that  muscarine  and  pilocarpine  act  on 
the  peripheral  end  of  the  sudorific  nerves. 

Quinine,  iodine,  arsenic,  and  mercury,  when  introduced  into  the 
body,  reappear  in  the  sweat. 

Although  the  nerves  of  the  sweat-glands  are  not  anatomically 
separated  from  others,  yet  their  concurrence  in  the  secretion  is  evident. 
In  cutting  the  cervical  sympathetic  in  a  horse  there  is  produced  uni- 
lateral sweating  (Dupuy).  According  to  the  increased  intensity  with 


SECRETION.  297 

which  the  cervical  sympathetic  is  galvanically  excited  through  the  skin 
of  man,  there  follows  a  lowered  or  increased  perspiration  of  the  corre- 
sponding side  of  the  face.  These  facts,  together  with  the  known  dila- 
tation of  the  cutaneous  vessels  in  profuse  perspiration,  show  the  influ- 
ence of  the  vasomotor  nerves. 

Groltz  and  others  have  shown  that  by  exciting  the  nerve  of  a  limb 
the  perspiration  of  it  can  be  increased  through  the  action  of  sudorific 
nerve-fibers.  The  same  results  have  been  attained  even  though  the 
limb  has  been  previously  amputated  and  therefore  no  longer  subject  to 
circulation.  It  appears  that  the  vasomotor  and  sudorific  nerve-fibers 
run  in  the  nerves  by  themselves. 

Stimulating  in  man  a  motor  nerve, — such  as  the  tibial,  median, 
or  facial, — the  part  corresponding  to  the  active  muscles  would  perspire, 
even  upon  the  side  not  excited. 

The  excretion  of  sweat  takes  place  through  vis  a  tergo,  aided  by 
the  concurring  contraction  of  the  interlaced  muscular  fibers  in  the 
glandular  glomerules.  Besides,  a  kind  of  aspiration  is  exercised  at  the 
mouth  of  the  gland  by  the  evaporation  of  the  liquid  which  arrives 
there.  It  is  for  this  latter  reason  that  air  saturated  with  vapor  slack- 
ens perspiration,  especially  when  the  other  causes  of  transpiration  do 
not  act  very  strongly. 

In  the  normal  state  the  sweat  and  urine  vary  in  quantity  with 
the  season;  in  the  spring  the  sweat  predominates  over  the  urine,  in 
winter  the  reverse  is  true.  There  is  an  inverse  relation  between  the 
sweat  and  intestinal  secretions.  There  is  a  very  noticeable  balancing 
between  the  sweats  and  diarrhoea  of  phthisis. 

By  varnishing  the  body  death  is  caused.  This  does  not  occur  ~by 
retention  of  poisonous  principles  in  the  blood.  There  are  functional 
troubles,  the  most  remarkable  of  which  is  the  cooling  of  the  body. 
This  cooling  is  due  to  vasodilation,  and  is  the  cause  of  death. 

There  seems  to  be  a  very  steady  relation  between  the  amount  of 
moisture  exhaled  from  the  lungs  and  the  secretion  of  sweat.  It  is  cal- 
culated in  general  that  the  perspiration  is  double  that  of  the  water 
from  the  lungs  and,  on  an  average,  one  sixty-fourth  of  the  weight  of 
the  body. 

Suppression  of  Sweat  by  Cold. — All  pathologists  recognize  cold 
as  the  cause  of  many  lesions  of  an  inflammatory  nature.  If  this  be 
true,  it  is  produced  not  by  suppression  of  sweat  alone.  It  is  prob- 
able that  there  is  a  transmission  of  impressions  by  the  skin-nerves  to 
the  nerve-centers.  These  impressions  generate,  by  an  obscure  patho- 
genic mechanism,  the  inflammations  of  the  viscera. 


298  PHYSIOLOGY. 

Role  of  Sweat-secretions. — The  sweat  is  an  important  means  for 
the  elimination  of  water  and  alkalies. 

It  is  also  of  very  great  use  in  the  excretion  of  fatty  volatile  acids 
introduced  into,  or  formed  in,  the  organism.  It  is  able  to  supplement 
the  urinary  secretion,  for  the  skin  is  vicarious  for  the  kidneys.  It  also 
carries  off  medicines  and  poisonous  principles.  It  regulates  animal 
heat,  since  the  evaporation  of  the  water  of  sweat  cools  the  body.  The 
secretion  of  sweat  is  independent  of  the  circulation;  however,  there 
exists  a  relationship  between  them.  Thus,  an  abundance  of  sweat 
requires  a  full,  free  circulation.  As  the  salivary  glands  need  a  flow  of 
blood  to  furnish  materials  for  secretion,  so  do  the  sweat-glands. 

I  have  shown  elsewhere  that  the  sudorific  centers  are  in  the 
spinal  cord  and  that  their  fibers  run  in  the  lateral  columns.  The 
sweat-centers  are  excited  by  an  excess  of  C02  in  the  blood  and  by  over- 
heated blood.  Camphor,  acetate  of  ammonium,  and  pilocarpine  excite 
sweat  by  a  direct  action  on  the  centers.  Muscarine  excites  sweat  by  a 
local  action;  atropine  arrests  it. 

Pathological. — Besides  the  components  mentioned,  biliary  pig- 
ment is  also  found  in  the  sweat  of  persons  having  jaundice;  sweat 
becomes  bitter  after  strong  doses  of  quinine  from  its  appearing  in 
this  medium  during  its  elimination  from  the  body.  The  sweat  of 
diabetes  is  found  to  be  sweetish,  although  the  presence  of  glucose  in 
it  has  not  been  definitely  determined.  The  red  pigmentation  some- 
times found  is  attributed  to  the  blood-globules,  crystals  of  which 
were  found  in  the  sweat.  Hebra  saw  it  succeed  menstruation;  but 
it  may  also  occur  in  serious  nervous  disease  and  in  yellow  fever.  In 
the  offensive  sweat  of  feet  there  is  found  leucin,  tyrosin,  baldrianic 
acid,  and  ammonia. 

THE  SECRETION  OF  THE  URINE. 

In  a  perfectly  normal  being  the  problems  of  wraste  and  repair 
are  balanced  to  a  nicety.  This  -equilibrium  owes  its  maintenance  to 
the  proper  action  of  the  various  glands  of  the  economy,  whether  secre- 
tory or  excretory.  As  we  know,  the  tissues  of  the  body  are  bathed  in 
lymph  containing  the  compounds  in  solution  that  are  necessary  for 
their  nourishment:  proteids,  carbohydrates,  fats,  salts,  and  gases. 
By  reason  of  the  organism  exercising  its  various  functions,  waste 
follows  in  direct  proportion  to  the  activity  of  the  tissues.  The  worn- 
out  and  effete  materials  first  find  their  way  into  the  lymph  and  from 
it  into  the  blood-stream,  to  be  later  eliminated  from  the  economy,  else 
deleterious  results  will  follow  their  retention  in  the  body.  It  is  by  the 


SECRETION.  399 

selective  action  of  the  cells  of  the  various  glands  of  the  body  that 
these  useless  substances  are  removed  from  the  blood :  that  is,  secreted 
by  them  and  converted  into  such  form  as  to  be  readily  removed  to 
the  exterior  of  the  organism  by  excretory  processes.  In  the  main,  the 
products  to  be  removed  are  urea  and  allied  nitrogenous  bodies,  carbon 
dioxide,  salts,  and  water.  Most  of  the  water,  salts,  urea,  and  allied 
substances  are  eliminated  as  components  of  the  urine  by  those  most 
important  organs,  the  kidneys.  These  organs  are  of  vital  importance, 
since  nearly  all  of  those  waste-products  containing  nitrogen  are  elim- 
inated in  the  urine. 

The  kidneys  secrete  the  urine.  Their  excretory  functions,  a  mat- 
ter of  everyday  observation,  represent  the  extent  of  their  external 
secretion ;  although  not  yet  definitely  settled,  the  consensus  of  opinion 
leans  toward  the  kidneys  possessing  an  internal  secretion  as  well. 

Morphology  of  the  Urinary  Apparatus. — The  secretory  organs  of 
the  urine  are  the  kidneys.  They,  two  in  number,  are  compound  tubu- 
lar glands,  situated  in  the  back  part  of  the  abdomen.  The  kidneys 
fire  extraperitoneal  organs,  lying  behind  the  peritoneum  and  resting 
upon  the  lumbar  portion  of  the  diaphragm  and  anterior  layer  of  the 
lumbar  fascia.'  The  upper  borders  of  the  kidneys  touch  a  plane  that  is 
on  a  level  with  the  upper  border  of  the  twelfth  dorsal  vertebra ;  their 
lower  extremities  are  on  a  level  with  the  third  lumbar  vertebra.  The 
right  kidney  is  usually  somewhat  lower  than  the  left,  probably  because 
of  the  pressure  exerted  by  the  liver,  against  whose  lower  surface  the 
kidney  rests.  In  front  it  is  in  relation  with  the  liver,  the  descending 
portion  of  the  duodenum,  and  the  hepatic  flexure  of  the  colon;  the 
left  kidney  lies  in  relation  with  the  fundus  of  the  stomach,  the  tail 
of  the  pancreas,  and  the  descending  colon.  Superiorly  lie  the  supra- 
renal bodies.  The  kidneys  are  incased  in  a  variable  quantity  of  fat 
and  loose  areolar  tissue,  to  which  has  been  given  the  name  perirenal  fat. 

The  kidneys  are  firm  organs,  of  variable  color,  between  light  red 
and  bluish,  according  to  the  degree  of  congestion ;  each  kidney  weighs 
about  four  and  one-half  ounces.  In  shape  they  resemble  a  bean,  their 
length  being  double  their  width;  each  kidney  is  about  four  inches  in 
length,  two  inches  in  width,  and  one  inch  in  thickness. 

The  internal  border  of  each  kidney  is  concave,  the  concavity  being 
directed  slightly  forward  and  downward.  This  portion  of  the  kidney 
is  divided  by  a  deep,  longitudinal  fissure,  bounded  by  a  prominent  an- 
terior and  posterior  lip.  The  fissure  is  known  as  the  hilus,  and  allows 
of  the  passage  of  the  vessels,  nerves,  and  ureter  to  and  from  the  sub- 
stance of  the  kidney.  Just  within  the  hilus  is  a  dilated  fossa  known 


300 


PHYSIOLOGY. 


as  the  sinus,  which  contains  the  renal  artery,  vein,  and  pelvis  of  the 
kidney.  The  relation  of  the  structures  passing  in  and  out  of  the  hilus 
from  before  backward  are :  vein  in  front,  artery  in  the  middle,  and  the 
duct,  or  ureter,  behind  and  toward  the  lower  part.  By  keeping  in 
mind  these  relations  one  will  be  able  to  distinguish  the  right  from 
the  left  kidney  after  their  removal  from  the  body. 


Fig.  67.— Relations  of  the  Kidney.     (After  SAPPEY.) 

1,  1,  The  two  kidneys.  2,  2,  Fibrous  capsules.  3,  Pelvis  of  the  kidney. 
4,  Ureter.  5,  Renal  artery.  6,  Renal  vein.  7,  Suprarenal  body.  8,  8,  Liver 
raised  to  show  relation  of  its  lower  surface  to  right  kidney.  9,  Gall-bladder. 
10,  Terminus  of  portal  vein.  11,  Origin  of  common  bile-duct.  12,  Spleen 
turned  outward  to  show  relations  with  left  kidney.  13,  Semicircular  pouch 
on  which  the  lower  end  of  the  spleen  rests.  14,  Abdominal  aorta.  15,  Vena 
cava  inferior.  16,  Left  spermatic  vein  and  artery.  17,  Right  spermatic  vein 
opening  into  vena  cava  inferior.  18,  Subperitoneal  fibrous  layer  or  fascia 
propria  dividing  to  form  renal  sheath.  19,  Lower  end  of  quadratus  lumborum 
muscle. 

In  the  funnel-shaped  cavity  of  the  renal  pelvis  is  the  ureter. 
From  the  kidney  it  passes  over  the  psoas  muscle,  converging  toward 
that  of  the  opposite  side  to  cross  the  external  iliac  artery  and  vein.  It 
opens  obliquely  into  the  base  of  the  urinary  bladder.  In  females  the 
ureter  embraces  the  neck  of  the  uterus.  The  ureters  have  an  average 
length  of  eighteen  inches  and  a  lumen  which  averages  that  of  a  goose- 
quill.  Just  before  piercing  the  bladder-wall  the  lumen  of  the  ureter 
becomes  appreciably  smaller. 


SECRETION.  301 

The  urinary  bladder,  situated  between  the  symphysis  pubis  and 
the  rectum  in  man,  between  the  symphysis  and  the  uterus  in  woman, 
is  held  in  position  by  the  urachus  and  lateral  ligaments.  Its  base 
rests  upon  the  perineum  and  anterior  wall  of  the  rectum  in  man,  upon 
the  anterior  wall  of  the  vagina  in  woman.  From  the  base  of  the  blad- 
der the  urethra  takes  its  origin. 

The  opening  for  the  latter  bears  such  a  relation  to  the  entrance 
into  the  bladder  of  the  two  ureters  that  there  is  formed  the  vesical 
triangle.  The  openings  for  the  ureters  are  about  sixty  millimeters 
apart. 

The  capacity  of  the  bladder  varies  with  its  extensibility,  so  that 
it  is  possible  for  the  viscus  to  be  so  distended  that  its  upper  border 
may  reach  the  umbilicus  or  even  the  epigastric  region.  Ordinarily  the 
capacity  in  both  sexes  is  about  a  pint. 

The  bladder  receives  its  Hood-supply  from  the  branches  of  the 
anterior  trunk  of  the  internal  iliac.  The  lymphatic  vessels  communi- 
cate with  the  lumbar  ganglia.  The  nerves  are  derived  from  the 
sympathetic,  the  sacral,  and  probably  some  fibers  from  the  pneumo- 
gastric  also. 

General  Structure  of  the  Kidney. — Beneath  the  perirenal  fat  lies 
the  proper  tunic,  or  covering,  of  the  kidney,  commonly  called  the 
capsule.  In  health  it  is  a  smooth,  thin,  but  tough,  fibrous  covering, 
closely  adherent  to  the  organ,  but  from  which  it  can  be  readily  stripped. 
By  reason  of  this  separation,  however,  fine  connective-tissue  processes 
and  minute  blood-vessels  are  torn  which  have  served  as  a  means  of 
attachment  for  the  capsule.  The  denuded  kidney  presents  a  smooth, 
even  surface  of  a  deep-red  color. 

For  a  proper  naked-eye  study  of  the  kidney  the  organ  must  be 
divided  longitudinally  from  the  hilus  to  its  outer  border,  and  the  fat 
and  areolar  tissue  must  be  removed  from  the  vessels  and  ureter.  It 
will  at  once  be  seen  that  the  kidney  is  composed  of  a  cavity,  somewhat 
centrally  located,  and  the  parenchyma  of  the  organ,  nearly  surrounding 
the  central  cavity.  This  compartment,  as  before  stated,  is  termed  the 
sinus,  and  is  lined  by  a  continuation  of  the  fibrous  covering  of  the 
kidney.  It  is  through  the  hilus  that  this  fibrous  covering  passes,  as 
do  the  renal  vessels  and  ureter. 

The  ureter,  upon  entering  the  sinus,  is  expanded  into  a  funnel- 
shaped  sac,  the  pelvis.  The  pelvis  soon  divides  into  several  branches 
of  smaller  size,  and  these  immediately  subdivide  into  from  eight  to 
twelve  infundibula,  or  calyces,  from  their  resemblance  to  cups.  Into 
each  calyx  there  projects  the  point  or  extremity  of  a  renal  pyramid. 


302 


PHYSIOLOGY. 


The  blood-vessels  lie  within  the  sinus,  between  its  wall  and  the  exterior 
of  the  pelvis,  before  subdividing  and  entering  the  parenchyma  of 
the  organ. 

The  parenchyma  is  seen  to  be  composed  of  two  portions,  an 
external,  investing  cortical  portion,  and  an  inner,  medullary,  or  pyram- 
idal portion. 


Fig.  68. — Section  of  Kidney.     (LANDOIS.) 

1,  Cortex.  I',  Medullary  rays.  1",  Labyrinth.  3,  Medulla.  2',  Papillary 
portion  of  medulla.  2",  Boundary  layer  of  medulla.  4,  Fat  of  renal  sinus 
5,  Artery.  A,  Branch  of  renal  artery.  U,  Ureter.  C,  Renal  calyx. 

The  cortex  is  light  brown  in  color,  granular,  and  very  friable. 
The  granular  aspect  is  due  to  the  presence  of  Malpighian  corpuscles, 
which  are  separated  at  regular  distances  by  medullary  rays,  or 
striae,  which  give  to  the  cortex  a  radiate  appearance.  The  boundary 
zone  is  darker,  and  also  striated  from  blood-vessels  and  uriniferous 
tubules.  It  is  through  this  portion  that  arteries  and  nerves  enter  and 
veins  and  lymphatics  pass  from  the  kidney. 


SECRETION. 


303 


The  medulla  is  composed  of  from  eight  to  twelve  pyramids,  or 
cones,  of  pale-red,  striated  tissue,  known  as  the  pyramids  of  Malpighi; 


Fig.  69.— Diagram  of  the  Course  of  Two  Uriniferous  Tubules.     (LANDors.) 

1,  Malpighian  tuft  surrounded  by  Bowman's  capsule.  2,  Constriction  on 
neck.  3,  Proximal  convoluted  tubule.  4,  Spiral  tubule.  5,  Descending  limb 
of  Henle's  loop-tube.  6,  Henle's  loop.  9,  Wavy  part  of  ascending  limb.  10, 
Irregular  tubule.  11,  Distal  convoluted  tubule.  12,  First  part  of  collecting 
tube.  13,  Straight  part  of  collecting  tube.  A,  Cortex.  B,  Boundary  zone.  C, 
Papillary  zone. 

their  number  depends  upon  the  number  of  lobes  composing  the  organ 
during  the  foetal  state.  It  is  the  apices  of  these  cones  which  dip  down 
into  the  calyces  of  the  pelvis. 


304 


PHYSIOLOGY. 


Minute  Anatomy. — The  kidneys  consist  of  numerous  tubular 
glands  intimately  united  together.  The  tubes,  known  as  tubuli  uri- 
niferi,  take  their  origin  in  the  labyrinth  of  the  cortex  as  distinct 
globular  dilatations,  each  of  which  is  known  as  Bowman's  capsule. 
The  capsule  surrounds  a  small,  red,  spherical  body  known  as  the 
glomerulus,  or  Malpighian  corpuscle,  after  Malpighi,  its  discoverer. 
The  capsule,  about  one  one-hundredth  of  an  inch  in  diameter,  is  con- 
stricted at  its  neck  to  form  a  tube.  Beyond  this  constriction  the 
tube  pursues  a  very  convoluted  course  through  a  considerable  extent  of 
the  cortical  area,  as  the  tubulus  contortus,  which  is  about  one  six- 


Fig.  70.     (LANDOIS.) 

II.  Bowman's  capsule  and  glomerulus.    a,  Vas  afferens.    e,  Vas  efferens. 
Jc,    Endothelium   of   the   capsule,     c,    Capillary    network    of    the    cortex,      h, 
Origin  of  a  convoluted  tubule. 

III.  "  Rodded  cells  "   from  a  convoluted  tubule.    2,   Seen  from  the  side, 
with,  g,  inner  granular  zone.     1,  Seen  from  the  surface. 

IV.  Cells  lining  Henle's  looped  tubule.    ' 

V.  Cells  of  a  collecting  tube. 

VI.  Section  of  an  excretory  tube. 

hundredth  of  an  inch  in  diameter.  Soon  the  convolutions  disappear 
to  give  place  to  a  more  or  less  spiral  tube  as  it  approaches  the  medulla : 
spiral  tube  of  Schaclwwa. 

At  the  boundary-line  between  cortex  and  medulla  the  tube  be- 
comes suddenly  smaller  and  is  now  perfectly  straight,  forming  the 
descending  limb  of  Henle's  loop,  dipping  down  for  a  considerable 
distance  into  the  pyramid.  By  the  sudden  changing  of  its  course 
backward,  but  still  parallel  with  its  original  course,  there  is  formed 
the  loop  of  Henle,  which,  continued  upward  to  the  cortex,  constitutes 
the  ascending  limb  of  Henle's  loop.  Ascending  into  the  cortex  it  be- 


SECRETION.  305 

comes  dilated,  irregular,  and  angular, — zigzag, — which  ends  in  the 
distal  convoluted  tube,  finally  to  terminate  in  a  short  curved  tube, 
which  empties  into  the  straight,  or  collecting,,  tube. 

The  collecting  tubes,  as  they  run  toward  the  medulla  of  the  kid- 
ney, unite  with  other  distal  convoluted  tubules.  They  also  unite  at 
acute  angles  with  adjacent  collecting  tubes  finally  to  pass  to  the 
papillae.  The  loops  of  Henle  and  the  collecting  tubes  constitute  the 
tubuli  recti.  Each  uriniferous  tubule  is  thus  completely  isolated  as 
far  as  the  junction  of  the  distal  contorted  tubes  with  the  collect- 
ing tube. 

A  portion  of  the  loops  of  Henle  and  the  upper  part  of  the  collect- 
ing tubes  form  the  little  cones  in  the  cortex,  visible  to  the  eye  and 
known  as  the  pyramids  of  Ferrein. 

The  Malpighian  corpuscle  consists  of  a  spherical  plexus  or  knot 
of  blood-vessels,  the  glomerulus,  which  is  inclosed  in  the  dilated  end 
of  the  urinary  tubule,  known  as  the  capsule  of  Bowman.  As  the 
capsule  has  been  infolded  by  the  glomerulus  being  pushed  into  it  (as 
one  would  infold  the  end  of  the  finger  of  a  glove  by  the  tip  of  one's 
finger) ,  it  follows  that  the  capsule  consists  of  two  layers.  The  internal 
one,  covering  the  glomerulus  closely,  is  formed  of  cubical  cells,  while 
the  external  one,  formed  of  flat,  polygonal  cells,  passes  on  into  the 
neck  and  thence  forms  the  wall  of  the  convoluted  tubule.  The  cells 
in  this  portion  of  the  tube  are  shaped  like  a  cone,  the  narrow  end  be- 
ing directed  toward  the  lumen  of  the  vessel ;  owing  to  the  fine,  longi- 
tudinal lines  upon  each  cell,  it  has  a  rodlike  appearance :  rodded  cell 

The  Blood-vessels. — The  renal  artery  divides  at  the  hilus  into 
four  or  five  branches.  '  The  four  or  five  main  branches  continue  to 
divide  and  subdivide  and  so  pass  into  the  parenchyma  of  the  organ. 
They  course  between  the  papilla  to  run  up  to  the  boundary  between 
the  medulla  and  cortex.  Here  the  vessels  bend  at  right  angles  to 
form  a  series  of  loops  or  arches,  their  convexity  toward  the  cortex 
of  the  kidney.  From  the  convex  sides  of  the  arches  there  spring  ves- 
sels at  regular  intervals  termed  interlobular,  or  radiate,  arteries.  They 
sometimes  run  up  so  as  to  divide  the  cortex  into  small  lobules,  coursing 
singly  between  each  two  medullary  rays.  These  radiate  arteries  give 
off  numerous  small  branches  which  run  at  right  angles,  each  one  enter- 
ing a  Malpighian  corpuscle.  It  is  usual  for  the  point  of  entrance 
of  the  artery  to  be  diametrically  opposite  the  point  of  origin  of  the 
urinary  tubule.  These  last-named  vessels,  the  vasa  efferentia,  break 
up  into  very  fine  vessels  within  the  capsule  to  constitute  the  glomerulus. 
They  are  supported  by  connective  tissue,  and  form  a  veritable  tuft  of 

20 


306 


PHYSIOLOGY. 


capillary  vessels.  It  is  of  interest  to  note  that  each  glomerulus  is 
covered, by  a  single  layer  of  flat,  nucleated.,  epithelial  cells,  these  even 
dipping  down  between  the  capillaries. 

s 


Fig.  71. — Blood-vessels  and  Uriniferous  Tubules  of  the  Kidney 
(Semidiagrammatic) .      (LANDOIS.) 

A,  Capillaries  of  the  cortex.  B,  Of  medulla,  a,  Interlobular  artery.  1, 
Vas  afferens.  2,  Vas  efferens.  r,  e,  Vasa  recta,  c,  Venas  rectae.  v,  v,  Inter- 
lobular vein,  i,  i,  Bowman's  capsule  and  glomerulus.  x,  x,  Convoluted 
tubules,  t,  t,  Henle's  loop,  o,  o,  Collecting  tubes.  O,  Excretory  tube. 


SECRETION. 


307 


From  the  center  of  the  glomemlus  there  proceeds  a  vessel  that 
is  somewhat  smaller  than  the  afferent  vessel,  known  as  the  efferent 
vessel;  it  is  a  vein,  and  leaves  the  capsule  very  close  to  the  point 
of  entrance  of  the  vas  afferens. 

The  efferent  vessel  also  divides  to  form  a  secondary  capillary 
network,  the  renal  portal  system,  with  elongated  meshes  in  the  situa- 
tion of  the  pyramids  of  Ferrein ;  from  this  plexus  arise  the  interlobular 
veins  which  run  parallel  to  the  interlobular  arteries. 


Fig.  72. — Longitudinal  Section  of  a  Malpighian  Pyramid.     (LANDOIS.) 

h,  Cortex,  i,  Boundary  or  marginal  zone,  k,  Papillary  zone.  PF,  Pyra- 
mids of  Ferrein.  RA,  Branch  of  renal  artery.  RV,  Lumen  of  renal  vein 
receiving  an  interlobular  vein.  ~VR,  Vasa  recta.  PA,  Apex  of  renal  papilla. 
b,  6,  Embrace  the  bases  of  the  renal  lobules. 

The  medulla  of  the  kidney  receives  its  arterial  supply  from  the 
arterice  rectce;  these  latter  are  vessels  which  spring  either  from  the 
arterial  arches  or  from  the  interlobular  arteries.  According  to  some 
authors,  they  may  be  derived  from  the  afferent  vessels  of  the  deepest 
and  largest  glomeruli.  Within  the  pyramids  the  arteriae  rectse  divide 
and  subdivide  to  form  a  plexus  of  capillaries  which  eventually  merge 
into  the  vence  rectce,  to  empty  into  the  venous  trunks  at  the  boundary 
between  the  medulla  and  cortex. 


308  PHYSIOLOGY. 

The  renal  veins  arise  from  three  sources:  (1)  the  venous  plexus 
beneath  the  capsule,  (2)  the  plexus  around  the  tubuli  contort!,  and 
(3)  the  plexus  located  near  the  apices  of  the  pyramids.  Within  the 
sinus  the  larger  branches  from  these  plexuses  inosculate  to  form  the 
renal  veins,  which  pass  through  the  hilus  to  empty  into  the  inferior 
vena  cava. 

The  vasa  recta  circulation  is  of  prime  importance  in  that  it 
forms  a  sidestream  through  which  much  blood  may  pass  without 
being  compelled  to  traverse  the  glomerulus.  It  is  very  apparent  that 
this  circulation  is  highly  useful  in  conditions  of  kidney  congestion  as 
a  sidestream. 

Three  kinds  of  capillaries  are  found  within  the  kidney:  (1) 
glomerular,  (2)  efferent  capillaries,  and  (3)  capillaries  of  the  vasce 
rectce.  The  kidney,  for  its  size,  is  abundantly  supplied  with  blood. 

Lymphatics. — The  kidneys  are  richly  supplied  with  lymphatics, 
occurring  as  slits.  The  renal  lymphatics  terminate  in  the  lumbar 
lymphatic  glands. 

Nerves. — The  nerves  of  the  kidney  accompany  its  blood-vessels, 
ganglionic  plexuses  being  numerous.  They  are  from  the  renal  plexus, 
coming  originally  from  the  solar  plexus. 

Physical  Properties  and  Chemical  Composition  of  the  Urine. 

The  analytical  study  of  the  urine  is  of  great  value  to  the  physi- 
cian and  surgeon  because  of  the  knowledge  which  it  gives  concerning 
the  processes  of  metabolism  occurring  within  the  body.  The  nature 
and  amount  of  the  various  end-products  of  metabolism  are  carefully 
investigated  as  they  occur  in  the  urine,  whether  they  be  normal  or 
pathological.  From  these  investigations  corresponding  conclusions 
are  drawn. 

Neutral  substances  are,  normally,  either  absent  or  present  in 
but  minutest  quantities.  All  of  the  important  and  more  abundant 
constituents  of  normal  urine  are  either  basic  or  acid  in  reaction. 
These  bases  and  acids  must,  therefore,  enter  into  various  combinations, 
making  the  urine  a  solution  of  salts.  The  quantity  of  separate  in- 
gredients found  analytically  might  lead  the  observer  to  consider  the 
metabolic  processes  as  pathological,  yet  in  solution  perfectly  normal 
compounds  are  formed  by  these  same  components.  The  error  is  due 
to  the  inability  to  study  the  properties  of  the  urine  as  a  complex  unit : 
the  effects  certain  components  have  on  others,  their  avidity  for  one 
another,  and  the  consequent  equilibrium  established. 


SECRETION.  309 

The  Urine. — The  normal  human  urine,  recently  passed,  is  a  clear 
liquid  of  a  straw  color.  It  has  an  average  specific  gravity  of  1.020,  is 
of  aromatic  odor,  and  a  salty  bitter  flavor.  In  reaction  it  is  acid; 
only  in  pathological  conditions  does  it  become  neutral  or  alkaline. 

Eeceding  from  the  temperature  of  about  100°  F.,  which  is  proper 
to  it  in  the  act  of  passing,  it  loses  its  aromatic  odor  and  acquires  a 
peculiar  odor,  described  as  urinous.  In  healthy  persons  it  has  been 
seen  to  be  phosphorescent  during  micturition,  probably  from  the 
liberation  of  phosphorus  by  its  salts.  In  cooling,  urine  becomes  tur- 
bid, with  a  small  cloud  suspended  in  the  thickness  of  the  liquid,  formed 
from  the  epithelium  of  the  uriniferous  tubules.  It  leaves,  besides, 
especially  if  very  much  colored,  sediments  of  different  appearance, 
according  to  the  varying  composition. 

The  quantity  of  urine  secreted  by  the  kidneys  of  a  healthy  adult 
man  in  twenty-four  hours  ranges  from  1200  to  1700  cubic  centimeters, 
or  about  50  ounces ;  in  females  the  quantity  is  less.  During  sleep  the 
amount  secreted  is  less  than  at  other  times,  so  that  the  minimum  secre- 
tion is  placed  between  2  and  4  A.M.  and  the  maximum  from  2  to  4  P.M. 

While  the  average  daily  secretion  is  placed  at  50  ounces,  yet  it 
must  be  borne  in  mind  that  this  quantity  is  not  fixed,  but  may  be 
very  variable,  dependent  upon  numerous  conditions. 

The  amount  of  urine  is  diminished  by  reason  of  profuse  sweating, 
extensive  diarrhoea,  thirst,  diminution  in  blood-pressure,  after  severe 
hemorrhage,  and  in  some  forms  of  kidney  disease. 

Increase  in  urinary  secretion  (polyuria)  is  produced  by  an  in- 
crease in  blood-pressure,  by  imbibing  excessive  draughts  of  liquids,  by 
any  condition  whereby  the  cutaneous  blood-supply  is  diminished  (cold 
will  do  this).  Polyuria  is  likewise  produced  by  the  administration 
of  drugs  which  raise  arterial  tension,  as  digitalis  and  alcohol,  and 
caffeine  and  sparteine,  which  stimulate  the  renal  cells. 

The  influence  of  the  nervous  s}7stem  upon  the  secretion  of  urine 
is  very  clearly  demonstrated  by  cases  of  hysteria.  Hysterical  patients 
void  excessive  amounts  of  a  very  pale,  watery  urine. 

The  specific  gravity,  as  previously  stated,  averages  1.020;  that 
is,  the  mean  between  1.015  and  1.020.  The  specific  gravity  varies 
inversely  to  the  quantity  excreted.  When,  for  any  reason  not  patho- 
logical, there  is  polyuria,  the  mark  drops  proportionately,  registering 
as  low  as  1.002.  As  a  result  of  profuse  sweating  and  abstinence  from 
liquids,  the  mark  may  reach  1.035  in  healthy  individuals. 

Acidity. — The  acidity  of  the  urine  is  chiefly  due  to  acid  phosphate 
of  sodium.  There  are  two  tides  in  the  acidity  of  the  urine.  During 


I 

310  PHYSIOLOGY. 

digestion  the  formation  of  the  hydrochloric  acid  in  the  stomach  frees 
certain  bases  in  the  blood,,  which,  when  excreted,  diminish  the  acid 
reaction  of  the  urine.  This  is  called  the  alkaline  tide.  The  acid  tide 
is  after  a  fast,  and  hence  occurs  early  in  the  morning. 

Ordinarily  it  should  be  remembered,  when  taking  the  specific 
gravity  of  urine,  that  anything  below  1.010  should  at  once  excite  sus- 
picion of  polyuria,  with  probably  albumin;  when  above  1.030,  diabetes 
mellitus  or  some  febrile  condition  may  be  present. 

The  urinometer  is  the  instrument  used  to  ascertain  the  density 
of  any  given  sample  of  urine,  and  is  so  graduated  that,  when  floating 
in  distilled  water,  it  registers  0  degree,  by  which  is  meant  1000.  The 
urine  is  placed  in  a  tall,  cylindrical  glass  of  proper  width  so  that 
the  urinometer  will  not  adhere  to  its  sides.  After  cessation  of  the 
oscillations  of  the  instrument,  the  observer  carefully  sights  along  the 
surface  of  the  urine  to  note  the  number  registered.  This  precaution 
is  taken  because  the  capillarity  along  the  stem  of  the  instrument 
causes  the  urine  to  rise. 

The  urine  is  composed  of  water  in  the  average  proportion  of 
96  per  cent.,  and  of  substances  dissolved  in  it  in  the  proportion  of  4 
per  cent.  Among  the  "substances  dissolved"  in  urine  we  find:  urea, 
uric,  hippuric,  lactic,  and  oxalic  acids,  and  ammonia;  also  creatin, 
chlorides,  sulphates,  phosphates,  with  the  bases — potassium,  sodium, 
calcium,  and  magnesium. 

Urea  (CO[NH2]2)  is  the  diamide  of  C02;   that  is,  a  carbamide. 

Urea  greatly  prevails  over  the  other  constituents  of  the  urine, 
since  in  normal  urine  it  forms  nearly  one-half  of  the  solids.  Nearly 
one-half  of  urea  is  nitrogen.  It  is  the  principal  representative  of 
the  waste  of  the  nitrogenous  tissues. 

Urea  is  inodorous,  fresh,  bitter,  neutral,  very  soluble  in  water 
and  alcohol,  but  almost  insoluble  in  ether.  It  crystallizes  quickly 
into  needles;  slowly,  into  quadrangular  prisms  of  the  rhombic  sys- 
tem. Urea  fuses  and  decomposes  at  248°  F.,  with  the  development 
of  ammonia. 

Urea  is  very  rich  in  nitrogen.  The  nitrogen  that  finds  its  way 
from  the  body  through  the  urine  as  a  vehicle  amounts  to  about  15 
grams  in  twenty-four  hours.  This  represents  practically  all  of  the 
nitrogenous  waste  of  the  economy,  since  less  than  1  gram  finds  egress 
from  all  other  channels  taken  collectively.  The  total  amount  of 
nitrogen  is  estimated  by  the  Kjeldahl  process. 

Among  the  combinations  with  acids  and  bases  of  which  urea 
is  capable,  those  with  nitric  and  oxalic  acids  are  important.  It  is 


SECRETION.  311 

precisely  these  which  are  most  commonly  employed  in  the  extraction 
of  urea.  With  nitric  acid,  nitrate  of  urea  is  formed,  which  crystal- 
lizes in  lozenge-shaped  crystals.  With  oxalic  acid,  urea  forms  urea 
oxalate,  and  crystallizes  into  flat  or  prismatic  bodies.  Both  types 
of  crystals  may  very  readily  be  demonstrated  by  placing  drops  of  urea 
beneath  cover-glasses  and  allow  drops  of  nitric  and  oxalic  acids, 
respectively,  to  flow  beneath  the  cover-glasses.  After  some  little 
time  crystals  of  the  respective  types  will  be  seen  to  form.  Besides 
being  free,  urea  is  also  found  combined  in  the  urine  with  sodium 
chloride. 

DECOMPOSITION  OF  UREA.  —  When  urea  is  heated,  vapors  of  am- 
monia are  evolved.  Urine  is  also  subject  to  an  alkaline  fermentation, 
due  to  the  micrococcus  urea?.  This  generally  follows  the  acid  fer- 
mentation, but  may  take  place  without  it,  in  the  bladder  as  well  as 
outside.  This  fermentation  is  accomplished  by  decomposition  of  the 
urea  into  carbonate  of  ammonia.  By  virtue  of  this  the  urine  is 
strongly  darkened,  becomes  alkaline,  putrescent,  and  forms  a  film  of 
bacteria  on  its  surface.  Urinals  always  have  an  ammoniacal  odor. 

Hypobromite  of  soda  decomposes  urea  as  follows  :  — 


C0<         2  +  3NaBrO  =  C02  +  N,  +  2H20  -f  3NaBr 

\  2 

Urea  Sodium  Carbonic       Nitrogen  Sodium 

hypobromite.  acid.  bromide. 

Upon  this  reaction  depends  an  estimation  of  the  amount  of  urea 
present  in  a  sample  of  urine.  The  calculation  is  made  in  units  of 
nitrogen-gas,  which  gas  rises'  in  small  bubbles  to  be  collected  and 
measured.  . 

The  constituents  of  urine  are  not  actually  formed  in  the  kidney 
itself,  as  bile  is  formed  in  the  liver,  but  are  formed  elsewhere.  The 
kidney  is  simply  the  place  where  the  constituents  are  picked  out  from 
the  blood  and  eliminated  from  the  body. 

Muscular  exercise  has  but  a  slight  effect  on  the  amount  of  urea 
excreted;  this  is  in  striking  contrast  to  the  quantity  of  carbonic  acid 
that  accompanies  muscular  exertion  to  find  exit  in  the  expired  air. 
Muscle-work  falls  upon  the  carbon  rather  than  upon  the  nitrogen  of 
the  muscle-substance. 

QUANTITY  or  UREA.  —  The  quantity  of  urea  excreted  daily  varies, 
but  may  be  averaged  as  500  grains.  According  to  Tschlenoff,  after 
a  meal  rich  in  proteids,  which  stimulate  proteid  metabolism,  there  are 
two  maxima  in  its  excretion.  The  first  takes  place  at  the  third  or 


312 


PHYSIOLOGY. 


fourth  hour  and  the  second  at  the  sixth  or  seventh  hour.  The  urea 
comes  from  proteid  metabolism,,  and  not  from  the  food.  Labor 
greatly  increases  the  exhalation  of  carbonic  acid,  but  does  not  affect 
to  any  great  extent  the  excretion  of  urea. 

FORMATION  OF  UREA. — The  chief  source  of  urea  is  from  the 
metabolism  of  the  muscles.  The  ingestion  of  a  large  amount  of  pro- 
teid food  stimulates  metabolism.  Muscles  contain  in  their  mass  over 
70  grams  of  creatin,  while  the  amount  of  creatin  excreted  is  only 
about  1  gram.  Urine  contains  about  30  grains  of  urea  and  muscles 


^X^\l 

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,   A*£:&i? 

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*. ,^S\^.    jA     JV    *    *  .   ^ 


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Fig.  73. — Uric-Acid  Crystals  with  Amorphous  Urates. 
(PuRDY,  after  Peyer.) 

only  a  trace.  But  all  experiments  to  prove  an  actual  relation  between 
creatin  and  urea  have  been  failures. 

The  other  alloxuric  bodies — xanthin,  hypoxanthin,  and  uric  acid- 
are  also  to  be  regarded.  They  are  members  of  a  group  of  bodies 
having  as  their  base  of  formation  the  so-called  purin-ring  which  con- 
sists of  two  urea  radicles  linked  together  by  a  central  chain  of  carbon 
atoms.  They  are  probably  split  up  in  part  into  urea. 

I  have  already  alluded  to  arginin  as  a  source  of  urea.  All  the 
proteids  are  probably  split  up  into  bodies  which  form  ammonia.  Now, 
if  we  give  by  the  mouth  ammonia  salts  we  find  an  increase  of  urea. 
Further,  if  ammonia  salts  are  perfused  through  the  liver  we  find  urea 


SECRETION.  313 

is  generated.  This  and  various  other  facts  lead  us  to  believe  that  the 
liver  is  the  chief  manufactory  of  urea. 

Uric  Acid  (C5H4N403). — This  constituent  is  scarce  in  human 
urine,  hardly  reaching  0.03  per  cent,  of  its  component  solids.  Next 
to  urea,  it  is  the  product  of  excretion  richest  in  nitrogen.  It  is  very 
preponderant  and  perhaps  altogether  the  chief  excretion  in  birds,  rep- 
tiles, and  insects. 

Uric  acid,  or  lithic  acid,  is  colorless,  inodorous,  and  insipid;  it 
usually  crystallizes  in  whetstone  crystals,  which  have  for  a  fundamental 
type  the  vertical  rhombic  prism.  It  is  insoluble  in  alcohol  and  ether, 
only  very  slightly  soluble  in  water.  The  rhombic  crystals  are  charac- 
teristic of  uric  acid. 

If  HC1  be  added  to  urine,  there  will  be  deposited  on  the  bottom 
of  the  vessel  after  several  hours  a  deposit  resembling  Cayenne  pepper. 
Uric  acid  occurs  in  the  urine  as  acid  sodium  urate.  The  HC1  de- 
composes the  urates,  setting  free  the  acid,  which  does  not  crystallize 
at  once,  by  reason  of  the  presence  of  phosphates.  According  to  Liebig, 
it  is  especially  by  the  phosphates  that  the  acid  is  dissolved,  under 
the  form  of  urate. 

Uric  acid  is  dibasic,  so  that  there  are  two  classes  of  urates :  the 
normal  urates  and  the  acid  urates.  The  amorphous  urates  are  quad- 
riurates;  acid  urates  are  crystalline. 

Uric  acid  is  trioxy-purin.  The  purin  bases  are  hypoxanthin. 
xanthin,  adenin,  guanin,  and  uric  acid.  All  these  bodies  are  derived 
from  a  substance  called  purin. 

The  elimination  of  nitrogen  in  the  urine  can  be  augmented  by  the 
food.  Thus,  nuclein  (of  which  the  thymus  contains  a  large  amount), 
coffee,  cocoa,  and  meat  (veal  and  ham  especially),  cheese,  and  beer 
are  rich  in  purins.  The  bodies  poor  in  purins  are  milk,  potatoes, 
white  bread,  rice,  eggs,  salads,  and  cabbage. 

FORMATION  OF  THE  URIC  ACID. — Like  with  urea,  the  liver  also 
forms  uric  acid  from  ammonia  and  lactic  acid.  It  is  a  result  of  pro- 
teid  metabolism,  especially  of  the  nuclein  of  the  cells.  Large  draughts 
of  water,  quinine,  and  common  salt  diminish  the  quantity  of  uric 
acid.  In  gout  the  amount  excreted  in  the  urine  is  small,  while  it  ac- 
cumulates in  the  blood  and  tissues.  Uric  acid  and  lithic  acid  are  the 
same.  Lateritious,  or  brick-dust,  sediment  in  the  urine  is  composed  of 
urates,  and  is  chiefly  sodium  urate. 

The  average  daily  quantity  of  uric  acid  passed  in  the  urine  of 
man  might  be  calculated  at  about  7  grains.  When  the  quantity  is 
excessive,  it  very  frequently  happens  that  the  acid  is  deposited  in  the 
form  of  urinary  calculi  and  gravel. 


314  PHYSIOLOGY. 

MUREXIDE  TEST. — Slowly  and  gently  heat  some  urine  and  nitric 
acid  in  a  porcelain  dish  to  the  point  of  dryness.  Decomposition  has 
taken  place,  the  color  changing  to  yellow,  and  N  and  C02  are  given 
off.  After  allowing  the  yellow  stain  to  cool,,  add  a  drop  of  dilute 
ammonia-water  to  it,  when  will  be  formed  with  the  uric  acid  a  purplish- 
red  color  of  murexide.  On  the  addition  of  caustic  potash  the  color 
becomes  a  marked  blue. 

Hippuric  Acid  (C9H9N03),  which  is  the  principal  representative 
of  nitrogenized  regression  in  the  herbivora,  is  scarce  in  human  urine. 
In  the  latter  it  appears  chiefly  after  the  use  of  some  fruits,  such  as 
apples,  plums,  and  grapes. 

Hippuric  acid  is  the  product  of  the  coupling  of  glycocin  with 
benzoic  acid.  It  may  also  be  formed  in  the  kidney  itself.  It  is  mono- 
basic, very  slightly  soluble  in  cold  water  and  ether,  and  readily  sol- 
uble in  warm  water  and  alcohol.  It  crystallizes  in  vertical  rhombic 
prisms,  is  of  a  bitterish  flavor,  and  is  acid  in  reaction.  When  decom- 
posed by  heating  with  acids  and  alkalies,  or  when  transformed  by 
animal  ferments,  hippuric  acid  resolves  itself  into  its  components: 
benzoic  acid  and  glycocin.  Ingested  benzoic  acid  and  oil  of  bitter 
almonds  are  eliminated  with  the  urine  as  hippuric  acid. 

Some  of  the  hippuric  acid,  at  least,  is  the  product  of  the  activity 
of  the  secreting  cells  of  the  renal  tubules,  as  is  demonstrated  by  per- 
fusing. If  arterial  blood  containing  benzoic  acid  and  glycocin  be 
forced  through  the  blood-vessels  of  a  freshly  excised  kidney,  hippuric 
acid  will  be  found  in  the  perfused  blood. 

The  food  of  herbivora  seems  to  be  an  important  factor  in  the 
manufacture  of  hippuric  acid.  When  fed  upon  grain  without  the 
husk,  hippuric  acid  is  absent.  Crystals  of  hippuric  acid  can  be  readily 
precipitated  from  the  fresh  urine  of  horses  and  cows. 

Lactic  Acid  is  a  constant  component  of  the  urine.     Its  quantity 
is  increased  when  it  abounds  in  the  blood  from  deficiency  of  oxidation, 
or   from   free   derivation   from   the   aliments,   or   from   gastric   f er- , 
mentations. 

Oxalic  Acid  is  an  inconstant  component;  it  occurs  with  calcium 
in  the  crystalline  form  of  octahedrons.  The  crystals  are  insoluble 
in  acetic  acid,  but  are  readily  dissolved  by  hydrochloric  and  nitric 
acids.  The  "  envelope  "-shaped  crystals  are  very  characteristic. 

Oxalic  acid  appears  to  be  derived  from  outside  the  economy, 
principally  from  the  ingestion  of  vegetable  foods,  such  as  sorrel, 
lemons,  rhubarb,  etc.  It  may  also  result  from  incomplete  oxidative 
processes. 


SECRETION. 


315 


Creatinin  occurs  in  the  urine  in  the  average  daily  amount  of  0.9 
grain.  Its  sources  are  believed  to  be:  (1)  the  creatin  of  muscles 
formed  by  the  subtraction  of  a  molecule  of  water  and  (2)  flesh  foods. 
If  creatin  be  fed  to  animals  it  appears  as  creatinin  in  the  urine; 
however,  if  it  be  injected  intravenously  it  appears  in  the  urine  as 
creatin;  so  that  it  is  very  improbable  that  the  kidneys  are  concerned 
in  its  manufacture. 

Xanthin,  hypoxanthin,  leucin  and  tyrosin,  and  traces  of  allantoin 
are  sometimes  formed  in  the  urine  where  they  represent  nitrogenized 
bases  of  albuminoid  retrogression.  Glycuronic  and  homogentisinic 


Fig.  74. — Leucin  in  Balls;    Tyrosin  in  Sheaves.     (PEYER.) 

acids  are  found  in  the  urine  occasionally.     Children  of  first  cousins 
almost  invariably  have  in  their  urine  homogentisinic  acid. 

Coloring  Matters  of  the  Urine. — The  two  main  coloring  matters 
of  the  urine  are  urochrome  and  urobilin.  Under  normal  physiological 
conditions,  urine  may  range  from  an  almost  colorless  or  pale  straw- 
yellow  through  intermediate  shades  until  reddish  brown  is  reached. 
The  commonest  condition  is  yellow.  Pale  urine  is  usually  of  low 
density ;  high-colored,  of  high  density,  dependent  upon  the  constituents 
excreted  by  the  renal  epithelium.  In  addition  to  the  two  main  color- 
ing matters  may  be  mentioned  uroerytlirin  and  licematoporpliyrin; 


316  PHYSIOLOGY. 

these  four  are  not  the  only  chromogenic  factors  in  the  urine,  but  are 
the  ones  that  are  best  known  to  us  to-day. 

UROBILIN,  like  bile-pigment,  is  an  iron-free  derivative  of  haemo- 
globin. In  normal  urine  it  occurs  in  very  small  amounts  and  almost 
always  as  a  cliromogen;  only  rarely  is  it  found  free  in  physiological 
urine.  In  diseases  it  is  commonly  increased,  especially  in  the  highly 
colored  urines  of  feverish  patients.  It  gives  to  the  urine  a  peculiar 
reddish  color. 

Urobilin  is  identical  with  stercobilin.  The  theory  usually  ac- 
cepted concerning  its  mode  of  origin  is  that  bile-pigment  is  converted 
in  the  intestines  into  stercobilin;  while  the  major  portion  of  the  ster- 
cobilin leaves  the  body  combined  with  the  faeces,  nevertheless  some  is 
reabsorlted  and  excreted  in  the  urine  as  urobilin.  Some  observers 
state  that  intestinal  micro-organisms  can  reduce  bilirubin  to  urobilin. 

UKOCHROME  is  regarded  as  the  proper  pigment  of  the  urine,  giving 
to  this  secretion  its  familiar  yellow  color.  When  removed  from  this 
medium  the  urine  loses  nearly  all  of  its  color.  It  is  separable  into 
yellow  scales.  Urochrome  may  decompose  to  produce  uromelanin, 
among  other  products.  The  last-named  constituent  gives  a  blackish 
tinge  to  the  urine. 

UROERYTHRIN. — Aqueous  solutions  of  urochrome,  when  exposed 
to  the  air  and  so  oxidized,  turn  red  (uroerythrin).  This  coloring 
matter  is  familiarly  known  by  reason  of  its  association  with  the  acid 
sodium  urates,  which  it  colors  red  to  form  the  popularly  known  "brick- 
dust"  sediment.  Normally,  it  occurs  in  but  small  quantities,  but  by 
reason  of  its  strong  coloring  properties  is  intimately  concerned  in  the 
coloring  of  the  urine.  Three  properties  are  characteristic  of  uroery- 
thrin: (1)  its  remarkable  affinity  for  uric-acid  compounds,  (2)  the 
ease  with  which  its  solutions  are  decolored  by  light,'  and  (3)  its 
color-reactions  with  caustic  alkalies  and  mineral  acids. 

H^EMATOPORPHYRIN  exists  in  but  very  small  amounts  in  the  urine 
normally;  pathologically  and  after  the  ingestion  of  certain  drugs,  as 
sulphonal,  it  may  be  greatly  increased. 

INDICAN,  OR  INDOXYL. — This  is  another  pigment  which  colors  the 
urine  intensely  yellow.  It  is  an  indigo  substance  represented  by  a 
dense,  yellow-brown  acid,  nauseatingly  bitter  and  very  soluble  in  water, 
alcohol,  and  ether. 

Indican  is  derived  from  indol,  which  is  formed  in  the  intestines  as 
a  product  of  putrid  decomposition  of  the  pancreo-peptones.  It  is  in 
direct  relation  to  the  quantity  of  bacterial  putrefaction  of  albumins. 
Indican  is  really  a  conjugated  sulphate. 


SECRETION.  317 

Test. — When  urine  is  mixed  with  an  equal  bulk  of  strong  HC1, 
indoxyl  is  liberated  from  the  sulphate.  A  solution  of  hypochlorite  is 
now  added,  drop  by  drop,  when  indigo-blue  will  be  formed  by  oxida- 
tion of  the  indoxyl.  Upon  the  addition  of  chloroform  the  blue  matter 
is  precipitated,  forming  a  layer  at  the  bottom  of  the  liquid. 

Pathological  Pigments. — BLOOD-PIGMENTS. — Blood  in  the  urine 
(haematuria)  may  result  from  injury  or  disease  anywhere  along  the 
urinary  tract.  In  this  urine  the  red  blood-corpuscles  are  found  in  the 
deposit.  An  idea  as  to  the  probable  source  of  the  haemorrhage  may 
be  gotten  by  careful  analysis.  Thus,  blood  from  the  kidney  is  usually 
small  in  amount,  gives  urine  a  "  smoky "  appearance,  and  is  well  mixed. 
Large  coagula  are  never  found  in  this  urine.  In  haemorrhage  from 
the  ureter  it  is  common  to  find  long,  wormlike  coagula.  Bladder 
haemorrhage  is  known  by  its  numerous  clots  and  shriveled-up  leuco- 
cytes. If  the  urine  be  alkaline,  crystals  of  triple  phosphate  will  likely 
be  found. 

In  hcemoglobinuria,  the  pigments  exist  in  solution,  no  corpuscles 
being  found.  It  is  caused  by  the  excretion  of  haemoglobin  by  the 
kidneys  when  it  exists  as  a  free  body  in  the  blood-stream.  Free 
haemoglobin  is  due  to  active  haemocytolysis,  as  injection  of  foreign 
blood,  severe  burns,  etc. 

BILE-PIGMENTS  IN  THE  URINE. — It  is  usually  in  cases  of  icterus 
that  this  condition  exists  when  the  urine  becomes  of  a  decided  yellow 
color.  The  pigment  usually  found  is  bilirubin. 

Bile-pigment  is  readily  detected  by  Gmelin's  reaction,  performed 
by  gently  pouring  the  urine  upon  the  surface  of  fuming  nitric  acid, 
when  a  green-colored  ring  appears. 

CARBOLURIA. — In  this  condition  the  urine  is  greenish  brown,  be- 
coming darker  upon  exposure  to  the  air.  It  occurs  either  after  poison- 
ing by  carbolic  acid  or  when  the  acid  has  been  administered  as  a  drug. 

DRUG-PIGMENTS. — After  the  administration  of  certain  drugs  the 
urine  is  sure  to  be  colored  differently  from  normal.  Those  which  do 
this  are  rhubarb,  haematoxylin,  santonin,  and  methylene  blue. 

The  Inorganic  Constituents. — These  are  derived  either  from  the 
aliments  with  which  they  are  introduced  into  the  body  or  they  are 
formed  in  the  organism  by  combination  with  bases  of  the  oxidized 
sulphur  and  alimentary  phosphorus.  They  are  eliminated  with  the 
urine  in  daily  amounts  from  16  to  24  grams. 

To  these  components  belong:  chlorine,  combined  chiefly  with 
sodium;  phosphoric  acid,  uniting  with  potassa,  soda,  calcium,  and 
magnesia  to  form  basic,  neutral,  and  acid  salts;  sulphuric  acid,  in  part 


318  PHYSIOLOGY. 

combined  with  alkalies  and  in  part  united  to  indol  and  phenol  in 
the  form  of  aromatic  substances  (Baumann).  The  chlorides  and  the 
major  portion  of  the  phosphates  come  from  the  blood;  the  sulphates 
and  the  remainder  of  the  phosphates  come  from  the  activities  of 
metabolism. 

CHLORIDES  occur  in  the  form  of  sodic  chloride.  The  average 
quantity  excreted  is  180  grains  daily.  If  the  chlorides  be  in  excess  in 
the  food,  not  so  much  is  given  out  in  the  urine  as  has  been  introduced, 
since  part  passes  oft'  through  the  skin  and  rectum,  while  another  part 
accumulates  in  the  tissues.  Some  is  decomposed  to  form  the  HC1 
of  the  gastric  juice.  Sodium  chloride  is  absent  in  early  stages  of 
pneumonia. 

PHOSPHORIC  ACID. — This  acid,  combined  to  form  the  alkaline 
and  earthy  phosphates,  appears  in  the  urine  in  the  daily  quantity  of 
about  2  grams.  The  phosphoric  acid  of  the  urine  is  -derived  princi- 
pally from  the  alimentary  phosphates. 

Hence  there  is  an  increase  of  phosphates  after  a  meal  composed 
principally  of  meat,  after  muscular  and  nervous  labor.  There  is 
pathological  increase  in  diseases  of  the  brain  and  in  osteomalacia ; 
there  is  diminution  in  pregnancy  by  reason  of  deposition  of  phosphate 
within  the  foetal  bones. 

THE  SULPHURIC  ACID  is  derived  from  the  liberation  and  oxi- 
dation of  tissue  sulphur.  Sulphuric  acid  occurs  in  the  urine  in 
combination  with  alkalies,  principally  sodium  and  potassium.  The 
sulphur  introduced  into  the  system  medically  finds  egress  mainly  in 
the  faeces,  as  it  does  not  easily  pass  into  the  blood.  From  this  it  is 
inferred  that  the  sulphur  eliminated  is  derived  especially  from  the 
transformation  of  the  tissue-pro teids.  It  runs  parallel  with  urea  ex- 
cretion. The  daily  quantity  of  sulphates  excreted  is  3  grams.  Proteid 
contains  1  per  cent,  of  sulphur  and  16  per  cent,  of  nitrogen. 

The  aromatic  sulphates  form  one-tenth  of  the  total  sulphates,  and 
arise  from  bacterial  putrefaction  within  the  intestinal  canal,  in  intes- 
tinal obstruction,  typhoid  fever,  etc.  The  chief  aromatic  (ethereal) 
sulphates  are  phenol  sulphate  of  potassium  and  indoxyl  sulphate  of 
potassium. 

CARBONIC  ACID  in  a  state  of  combination  is  scarce  in  the  urine 
and  only  increases  there  after  the  use  of  alkaline  carbonates  and  of 
vegetable  acids,  which  latter  are  transformed  into  carbonic  acid  by  oxi- 
dation. 

To  sum  up  in  an  approximate  average  the  very  variable  propor- 
tions of  the  principal,  normal  constituents  of  the  urine,  it  may  be  said 


SECRETION.  319 

that  with  a  mixed  diet  and  moderate  bodily  movement  there  are  in 
every  100  cubic  centimeters  of  daily  urine : — 

Water   96.00  grams. 

Solid  components   4.00        " 

Urea    2.30 

Uric  acid    0.03    gram. 

Sodium  chloride    0.80 

Phosphoric  acid  0.15 

Sulphuric  acid   0.20 

Earthy  phosphates  0.08 

Ammonia   0.04        " 

Fermentation  of  Urine. — We  have  seen  that  the  reaction  of  urine 
is  generally  acid ;  but  it  can  become  alkaline,  even  in  the  physiological 
state,  from  abundant  ingestion  of  alkalies,  or  of  salts  with  organic 
acid.  The  intensity  of  the  acid  or  alkaline  reaction  of  urine  must 
necessarily  vary,  not  only  with  the  proportion  of  the  components  that 
determine  it,  but  also  with  the  degree  of  dilution. 

The  acidity  of  the  urine  may,  however,  be  further  increased  by  a 
process  of  acid  fermentation  due  to  bacteria,  in  the  presence,  perhaps, 
of  vesical  mucus.  This  fermentation  may  take  place  outside  of  the 
bladder  as  well,  for  we  see  the  acidity  of  the  urine  continue  to  increase 
from  the  time  of  emission. 

The  process  of  acid  fermentation  is  finally  accompanied  with 
development  of  a  mycelium  whose  spore  is  smaller  than  that  of  torula. 
It  appears  that  with  the  initiation  of  this  process  the  urine  absorbs 
oxygen  much  more  actively  (Pasteur). 

The  urine  is  also  subject  to  an  alkaline  fermentation  due  to  an 
enzyme,  urease,  of  the  micrococcus  urea?.  It  generally  follows  the  acid 
fermentation,  but  may  occur  without  it,  in  the  bladder  as  well  as 
outside.  The  urine,  after  prolonged  exposure,  especially  in  a  warm 
atmosphere,  has  been  found  to  become  neutral  and  then  gradually  alka- 
line. This  fermentation  is  accompanied  with  decomposition  of  the 
urea  into  ammonium  carbonate,  by  which  the  urine  is  strongly  dark- 
ened and  becomes  alkaline  and  of  a  strong,  putrid,  ammoniacal  odor. 

In  disease  of  the  urinary  apparatus,  and  especially  in  vesical 
inflammation  and  catarrhs,  the  process  of  ammoniacal  fermentation  is 
already  advanced  in  the  urine  at  the  time  of  its  passage.  In  this  case, 
epithelial  mucus  and  purulent  elements  aid  in  making  it  turbid. 

On  the  basis  of  the  preponderance  of  one  group  of  combinations 
over  another,  they  are  divided  into  uric,  oxalic,  and  phosphoric  sedi- 
ments. 


320 


PHYSIOLOGY. 


Umc  SEDIMENTS. — These,  composed  of  uric  acid  and  the  alkaline 
and  earthy  urates,  increase  the  acidity  of  the  urine,  render  it  muddy, 
and  impart  to  it  a  brick-red  color,  which  is  made  more  intense  by 
exposure  to  the  air.  With  the  microscope  the  observer  recognizes  in 
the  sediment  the  characteristic  crystals  of  uric  acid. 

The  precipitation  of  urates  within  the  bladder  is  very  probably 
caused  by  concentration  from  the  absorption  of  water  from  the  urine. 
The  common  belief  that  holding  the  urine  predisposes  to  stone  is, 
therefore,  justified.  Another  and  more  frequent  cause  of  uric  sedi- 
ments in  the  bladder  is  the  acid  fermentation  which  may  occur  there 


Fig.  75. — Crystals  of  Ammoiiio-magnesium  Phosphate.    (After  ULTZMANN.) 
1,  Crystals  in  rosette  shape.     2,   Crystals  in  coffin-lid  shape. 

from  the  presence  of  mucus,  as  in  vesical  catarrh.  These  are  strong 
predisposing  causes  to  uric  calculi. 

OXALIC  SEDIMENTS. — These  accompany  the  uric  sediments,  but 
there  may  be  a  predominance  of  oxalic  acid  combined  with  lime.  This 
sediment  is  recognized  by  its  crystals  of  calcium  oxalate,  the  "envelope" 
crystals.  They  are  insoluble  in  acetic  acid. 

They  are  chiefly  observed  in  deficient  respiration,  in  rickets,  in 
epileptiform  convulsions,  and  in  convalescence  from  serious  diseases. 
The  crystals  are  precipitated  by  neutralizing  the  acid  urine.  This 
explains  why  uric  calculi  are  often  mixed  with  oxalic  sediments.  The 
acid  urine,  with  its  uric  sediment,  readily  becomes  neutral  and  alkaline 


SECRETION.  321 

by  reason  of  purulent  catarrh  with,  therefore,  succeeding  precipita- 
tion of  the  oxalates. 

PHOSPHORIC  SEDIMENTS. — The  phosphoric  sediments  consist 
chiefly  of  crystallized  ammonio-magnesium  phosphate,  coffin-lid  shaped 
crystals,  and  of  calcium  phosphate. 

The  phosphoric  sediments  are  readily  distinguished  by  the  alkaline 
reaction  of  the  urine  and  by  their  insolubility  by  heat  (by  which  the 
urates  are  dissolved),  and  phosphoric  crystals  are  distinguished  from 
oxalic  by  their  solubility  in  acetic  acid. 

The  phosphoric  sediments  acquire  importance  only  when  they  are 
formed  within  the  bladder,  either  by  purulent  products  or  by  excessive 
retention  of  urine,  as  in  paralysis. 

Exceptional  or  Pathological  Components. — Besides  the  ordinary 
constituents  of  the  urine,  there  may  at  times  be  found  in  it  exceptional 
ones  of  pathological  significance. 

ALBUMIN. — Albumin,  and  more  properly  albumin  of  Hood-serum., 
is  an  abnormal  component  of  the  urine  which  has  great  importance  for 
the  physician.  Its  presence  in  this  secretion  gives  the  clinical  condition 
commonly  termed  albuminuria.  Its  presence  is  due  to  a  great  number 
and  variety  of  causes,  a  few  of  which  are:  (1)  temporary  or  lasting 
increase  of  pressure  of  the  blood  within  the  renal  system,  especially 
in  hypera?mia  from  cardiac  defect;  (2)  in  exanthemata  (scarlatina) 
and  other  febrile  diseases  in  general  (pneumonitis,  typhus,  pyaemia) ; 
(3)  inflammation  and  degeneration  of  the  kidneys,  as  well  as  in  dis- 
turbances and  inflammation  of  the  brain  and  in  epilepsy;  (4)  any 
substance  which  acts  upon  the  vascular  system  of  the  kidneys,  as  diu- 
retics, mercurials,  and  cantharides. 

The  recognition  of  albumin  in  the  urine  requires  care,  and,  above 
all,  it  is  necessary  to  remember  some  of  the  reactions  that  occur  in  the 
urine.  If  the  urine  be  acid,  the  albumin  accidentally  contained  there 
coagulates  at  temperatures  above  70°  C.,  the  coagulation  first  showing 
as  an  opacity  upon  the  surface  of  the  liquid. 

Again,  if  the  urine  be  alkaline  and  then  subjected  to  heat,  there 
may  result  a  marked  opacity  without  the  presence  of  albumin,  the 
darkening  being  caused  by  precipitation  of  phosphates.  To  differ- 
entiate from  phosphates,  a  few  drops  of  acetic  acid  are  added,  which 
immediately  dissolve  them. 

Heller's  Nitric- Acid  Test. — Albumin  is  also  recognized  by  means 
of  adding  one-fourth  of  the  proper  volume  of  HNX)3.  The  reaction, 
a  ring  of  white  precipitate  occurring  at  the  junction  of  the  two  liquids, 
is  evident  when  there  is  much  albumin.  If,  instead,  the  quantity 


322  PHYSIOLOGY. 

should  be  small  and  the  urine  concentrated,  nitrate  of  urea  will  be 
precipitated,  giving  an  erroneous  impression  to  the  observer.  If  the 
urine  be  diluted  one-fourth  with  water,  the  urea  precipitate  disappears.. 

A  method  of  measuring  the  quantity  of  albumin  present  in  urine 
is  easily  accomplished  by  the  method  devised  by  Esbach.  The  essen- 
tial principle  is  precipitation  of  the  albumin  by  means  of  Esbach's 
reagent,  which  in  1000  cubic  centimeters  of  water  contains  10  grams 
of  picric  acid  and  20  grams  of  citric  acid.  This  is  performed  in  a 
test-tube  so  graduated  that  the  figures  represent  grams  of  dried 
albumin  in  a  liter  of  urine.  It  is  essential  that  the  reaction  be  allowed 
to  proceed  for  twenty-four  hours  before  any  readings  are  taken. 

Proteoses  are  detected  by  the  precipitates  produced  by  nitric  and 
salicyl-sulphonic  acids  clearing  up  on  heating  the  urine  and  returning 
when  it  is  cooled. 

SUGAR. — While  it  is  known  that  normal  urine  may  contain  traces 
of  sugar,  attention  is  required  with  the  sugar  that  occurs  in  excess, 
especially  from  the  disease  known  as  diabetes  mellitus. 

In  the  first  place,  diabetic  urine  is  abnormal  in  amount,  even 
reaching  10  liters  a  day.  It  has  a  high  specific  gravity,  and  is  of  a 
pale  and  greenish  yellow,  so  that  sugar  may  be  suspected  at  once; 
when  the  increased  density  is  due  to  urea  the  urine  is  intensely  red- 
dish. However,  it  must  be  remembered  that  the  nitrogenous  excreta 
are  also  increased. 

The  sugar  present  is  in  the  form  of  dextrose.,  or  grape-sugar.  It 
is  increased  with  a  carbohydrate  diet  and  diminished  with  one  that  is 
nitrogenous.  Upon  standing,  there  are  developed  in  diabetic  urine 
torulce. 

Feliling's  Test. — Eesults  are  obtained  by  the  use  of  Fehling's 
solution.  This  is  an  alkaline  solution  of  copper  sulphate  to  which 
Rochelle  salt  has  been  added.  The  latter  holds  the  cupric  hydrate  in1 
solution.  The  presence  of  sugar  is  denoted  by  the  reduction  on  boil- 
ing of  yellow  precipitate  of  cuprous  oxide. 

Plienylhydrazin  Test. — This  is,  perhaps,  the  most  trustworthy 
of  all  the  sugar  tests.  It  depends  upon  the  formation  of  a  very  charac- 
teristic body  from  phenylhydrazin  hydrochloride  and  sodium  acetate: 
phenylglucosazone.  The  resultant  body  is  found  as  yellow  crystals, 
for  the  most  part  arranged  in  rosettes  and  clusters.  They  are  only 
sparingly  soluble  in  water.  The  characteristic  crystals  are  readily 
detected  under  the  microscope. 

The  phenylhydrazin  test  takes  place  with  glucose,  laevulose,  and 
glycuronic  acid. 


SECRETION. 


323 


Fermentation  Test  for  Sugar. — With  an  Einhorn  saccharometer 
tube  introduce  a  definite  quantity  of  urine  and  a  piece  of  Fleischman's 
yeast  about  the  size  of  a  pea;  then  stand  in  a  warm  place.  Next 
morning  read  off  the  percentage  of  glucose  on  the  instrument.  The 
fermentation  test  of  glucose  excludes  glycuronic  acid,  as  it  will  not 
ferment. 

BILE  and  BLOOD  in  the  urine  have  been  previously  discussed. 

TUBE-CASTS. — Cylinders,  or  casts,  of  the  uriniferous  tubules  are 
of  prime  importance  to  the  physician  in  his  diagnosis  of  some  forms 


Fig.  76. — Crystals  of  Phenylglucosazone.     (PURDY,  after  v.  Jaksch.) 

of  renal  disease.  Those  which  are  straight  may  be  said  to  be  casts  of 
the  collecting  tubes;  the  more  curved  and  twisted  ones  are  probably 
from  the  convoluted  tubules.  Various  kinds  of  casts,  or  cylinders,  are 
distinguished. 

Theory  of  the  Urinary  Secretion. 

The  theory  of  the  urinary  secretion  is  summed  up  by  regarding 
the  water  (which  determines  the  quantity  of  the  urine)  and  its  salts  as 
a  product  of  filtration  from  the  renal  glomerules;  the  dissolved  com- 
ponents (as  urea,  uric  acid,  etc.)  as  products  of  the  special  activity  of 
the  elements  of  the  epithelium  of  the  contorted  tubules. 


324  PHYSIOLOGY. 

That  the  passage  of  the  water  takes  place  chiefly  by  filtration  is 
shown  by  the  fact  that  the  quickness  of  this  passage  is  kept  in  direct 
relation  with  the  pressure  of  the  blood  in  the  renal  arteries,  and  the 
glomerules-  in  particular,  from  whose  vessels  the  watery  element  of  the 
urine  is  chiefly  derived. 

Nevertheless,  hydrostatic  pressure  is  not  the  only  factor  at  work 
in  the  glomerules,  for  their  epithelium  exerts  both  a  positive  and  a 
negative  influence:  positive  in  that  some  of  the  salts  of  the  urine 
are  here  secreted;  negative,  in  that  the  serum-albumin  of  the  blood  is 
prevented  from  passing  through. 

In  support  of  the  part  that  blood-pressure  bears  to  secretion  it 
has  been  noted  that,  when  the  total  contents  of  the  vascular  apparatus 
are  increased  so  that  blood-pressure  also  increases,  there  follows  an 
increased  secretion;  that  increased  action  of  the  heart  increases  the 
amount  of  urine;  and  that  variations  in  the  caliber  of  the  renal 
artery  give  proportionate  urinary  secretions. 

The  diuretics  made  use  of  by  the  physicians  owe  their  efficiency 
mainly  to  the  foregoing  principles.  Digitalis  increases  the  quantity 
of  urine  by  raising  the  blood-pressure,  whereas  urea,  potassium  ni- 
trate, caffeine,  and  other  drugs  act  upon  the  rodded  epithelium  of  the 
tubuli  contorti. 

It  must  not  be  forgotten  that  at  all  times  there  is  glomerular 
pressure  by  reason  of  the  vasa  efferentia  being  of  smaller  lumen  than 
that  of  the  afferentia. 

Colheim  and  Roy,  in  their  experiments  with  the  oncometer,  have 
noted  that  the  curve  representing  the  volume  of  the  kidneys  runs 
parallel  with  the  curve  of  arterial  pressure ;  it  has  smaller  oscillations, 
both  respiratory  and  cardiac.  The  nervous  influences  acting  upon 
the  renal  secretion  are  vasomotor;  existence  of  the  so-called  secretory 
nerves  has  not  yet  been  definitely  demonstrated. 

Toxicity  of  the  Urine. — After  the  ablation  of  the  two  kidneys 
the  animal  dies  from  uraemia ;  that  is,  there  is  an  accumulation  of  the 
urinary  products  in  the  blood.  The  removal  of  one  kidney  is  not 
necessarily  fatal.  The  urine  of  daytime  is  more  toxic  than  at  night ; 
it  is  especially  narcotic,  while  night  urine  is  more  convulsivant.  A 
man  excretes  enough  poisonous  material  by  the  kidneys  in  two  days 
to  cause  death.  When  there  is  an  excess  of  urea  in  the  blood,  the 
disease  is  termed  uraemia.  The  toxic  substance  is  probably  not  urea, 
but  some  other  organic  body.  The  usual  cause  of  uraamia  is  Bright's 
disease.  Uric  acid  in  excess  is  supposed  to  be  the  cause  of  rheumatism 
and  gout. 


SECRETION.  325 

Influence  of  the  Nerves  Upon  the  Secretion  of  Urine. — As  has 

been  elsewhere  stated,  the  nerves  of  the  kidneys  are  derived  from  the 
renal  plexus  and  are  composed  of  both  medullated  and  nonmedullated 
fibers  with  nerve-cells.  These  are  both  vasodilator  and  vasoconstrictor 
in  function.  As  yet,  no  true  secretory  nerves  are  known,  so  that  it  is 
by  the  influence  of  the  vasomotor  nerves  distributed  along  the  course 
of  the  renal  vessels  that  variations  in  the  amount  of  urine  secreted 
occur.  Thus,  the  amount  of  urine  secreted  depends  upon  the  pressure 
of  the  blood  circulating  through  the  capillaries. 

Frequent  and  small  urinations,  under  mental  apprehension,  show 
a  very  probable  nervous  influence  upon  the  excretion  of  the  urine. 
Polyuria  and  the  peculiar  aspect  of  the  urines  of  hysteria  are  also 
known ;  whether  these  peculiarities  are  dependent  upon  direct  nervous 
influence  upon  the  secretion  is  not  known.  Ludwig  believes  that  the 
cause  lies  in  the  increased  pressure  in  the  renal  arteries  from  spastic 
contraction  of  other  vascular  regions. 

Injury  by  puncture  of  the  vasomotor  center  in  the  floor  of  the 
fourth  ventricle  likewise  is  followed  by  polyuria,  accompanied  by 
hsematuria  and  albuminuria.  By  this  experiment  it  is  demonstrated 
that  variations  in  urinary  secretion  are,  for  the  most  part,  very  inti- 
mately concerned  with  vasomotor  innervation. 

If,  while  the  renal  vasomotors  are  paralyzed,  the  majority  of  the 
vasomotor  nerves  of  the  entire  body  be  also  paralyzed  (as  by  section  of 
the  medulla),  there  follows  a  general  dilatation  of  the  arterioles  and 
capillaries  of  the  body.  This  causes  such  a  decided  fall  in  the  blood- 
pressure  that  the  amount  of  urine  secreted  is  much  diminished  or 
entirely  absent. 

However,  secretion  is  not  suspended  by  removal  of  the  brain,  nor 
destruction  of  the  spinal  cord  below  the  cervical  portion,  provided  that 
the  medulla  is  intact  and  with  it  the  respiration  and  circulation. 
(Krimer.) 

Urinary  Excretory  Apparatus. — After  the  urine  has  been  secreted 
by  the  kidneys,  it  must  needs  be  carried  away  from  the  body,  so  that 
the  economy  may  not  suffer  from  resorption  of  contained  toxic  prin- 
ciples, as  well  as  not  to  interfere  with  the  renal  action  by  equalizing 
pressure  within  that  organ  from  damming  back  of  the  urine. 

The  excretory  apparatus  comprises  the  ureters,  bladder,  and 
urethra. 

THE  URETERS  are  two  cylindrical  membranous  tubes  of  the  diam- 
eter of  a  goose-quill  and  about  twelve  inches  long.  They  extend  from 
the  pelvis  of  the  kidney  to  the  bladder,  to  which  viscus  runs  the  urine 


326  PHYSIOLOGY. 

from  the  kidneys.  The  general  course  of  each  ureter  is  downward 
and  inward  toward  the  median  line,  to  empty  into  the  base  of  the 
bladder  by  a  constricted,  slitlike  orifice.  The  ureter  runs  for  nearly 
an  inch  between  the  muscular  and  mucous  coats  of  the  bladder  before 
it  makes  its  exit  upon  the  inner  wall  of  the  organ. 

Structure. — The  ureter  is  composed  of  three  coats,  or  layers: 
serous,  or  adventitia;  muscular;  and  mucous. 

The  adventitia  is  continuous  with  the  capsule  of  the  kidney  at  one 
end  and  with  the  fibrous  layer  of  the  bladder  at  the  other.  In  it  are 
found  its  larger  vessels  and  nerves. 

The  muscular  coat  comprises  the  two  usually  distinct  muscular 
layers:  an  external  longitudinal;  an  internal,  circular  one. 

The  mucous  coat,  continuous  with  that  of  the  bladder,  lines  the 
ureter.  It  is  composed  of  stratified  epithelial  cells. 

Movement  of  the  Urine. — The  urine  flows  into  the  tubules  by  the 
vis-a-tergo  pressure  of  the  blood  in  the  afferent  capillaries.  This 
averages  from  120  to  140  millimeters  of  mercury.  This  force,  which 
is  capable  of  making  the  urine  flow  through  the  tubules,  is  incapable 
of  forcing  the  urine  through  the  ureters.  By  reason  of  the  ureters 
taking  a  diagonal  course  through  the  vesical  wall,  the  weight  of  the 
urine  already  in  the  bladder  must  exert  a  certain  amount  of  pressure 
upon  this  portion  of  each  ureter.  To  overcome  this  some  auxiliary 
force  must  be  called  into  action,  which  is  the  peristaltic  contraction 
of  the  ureters.  This  movement  begins  at  the  kidneys  and  is  trans- 
mitted (with  a  speed  of  from  20  to  30  millimeters  per  second)  down- 
ward into  the  bladder.  With  the  completion  of  each  peristaltic  move- 
ment there  exudes  into  the  bladder  a  drop  of  urine.  The  movements 
of  the  two  ureters  are  not  synchronous ;  they  are  reflex,  being  caused  by 
the  presence  of  urine  in  the  lumen  of  the  ureter. 

In  a  case  of  Dr.  W.  Easterly  Ashton's,  where  the  ureters  opened 
on  the  abdominal  surface,  I  counted  an  emission  of  urine  by  the 
ureter  every  twenty-four  seconds. 

The  greater  the  distension  of  the  lumen  of  the  ureter,  the  more 
rapid  will  the  number  of  peristaltic  movements  become. 

Experimentally,  peristaltic  movements  may  be  aroused  by  elec- 
trical or  mechanical  excitation;  movements  always  begin  at  the  point 
excited  and  proceed  toward  both  ends. 

THE  URINARY  BLADDER. — The  bladder  is  a  musculo-membra- 
nous  pouch  which  serves  as  a  temporary  reservoir  for  the  urine.  It  lies 
behind  the  pubis  and  within  the  pelvic  cavity  while  the  viscus  is 


SECRETION.  327 

empty,  but  when  distended  protrudes  into  the  hypogastric  region,  in 
extreme  cases  even  up  to  the  umbilicus. 

In  the  cat,  two  days  after  section  of  the  spinal  cord  above  the 
vesico-spinal  center  I  found  that  a  pressure  of  140  millimeters  of 
water  was  required  to  overcome  the  tonus  of  the  sphincter  when  a 
cannula  was  bound  in  the  urethra. 

Micturition. — When  the  act  of  micturition  takes  place  the  spinal 
detrusor  center  is  excited  into  activity  by  the  pressure  of  the  urine; 
the  sphincter  reflex  center  is  also  independently  excited  by  the  pressure 
of  the  urine,  and  opens  to  expel  the  secretion.  The  spinal  detrusor 
and  spinal  sphincter  are  under  the  control  of  a  cerebral  detrusor  center 
which  I  have  shown  to  be  seated  in  the  locus  niger,  which  is  set  in 
activity  by  the  cerebral  hemisphere  in  voluntary  micturition. 

Voluntary  micturition  is  materially  aided  by  the  action  of  the 
abdominal  and  respiratory  muscles. 


CHAPTER  IX. 

METABOLISM. 

THE  food  that  has  been  properly  digested  within  the  stomach 
and  intestines  is  absorbed  by  the  chyle  vessels  and  the  small  capil- 
laries by  whose  union  is  formed  the  portal  vein.  When  once  in  the 
blood-stream,  it  circulates  with  the  blood-current,  which  carries  it 
to  all  of  the  various  organs  and  tissues  of  the  body.  The  absorbed 
nutritive  products  are  held  in  solution  within  the  plasma  of  the 
blood. 

In  order  to  nourish  the  structures  outside  of  the  vessel-walls, 
the  plasma  with  its  contained  nourishment  is  constantly  being  dia- 
lyzed  through  the  capillary  walls  into  the  spaces  between  the  living 
cells.  By  this  provision  each  cell  is  bathed  in  a  plentiful  supply  of 
plasma,  from  which  medium  it  absorbs  its  nutriment. 

The  various  stages  of  the  nutritive  process — viz. :  the  transuda- 
tion  of  the  nutritive  plasma  from  the  blood,  the  assimilation  of  parts 
of  this  by  the  tissues  under  repair,  the  absorption  of  the  other 
portion  by  the  lymphatics,  and,  last,  the  reabsorption  of  the  final 
residue  together  with  that  of  the  waste-products  of  the  tissues  by  the 
veins — are  performed  simultaneously  and  continuously  in  the  living 
body.  With  the  entire  organism  in  a  healthy  condition  there  is  a 
perfect  balance  of  action. 

Action  and  use  are  always  followed  by  a  corresponding  amount 
of  waste.  The  machinist  must  be  making  repairs  to  the  locomotive 
or  other  machine  that  is  in  use.  So  the  tissues  of  the  body  are  con- 
tinually being  destroyed,  to  pass  away  as  effete  matters  due  to  exer- 
cise and  action  of  the  various  organs  and  parts  of  the  economy. 
Thus,  the  simple  movement  of  the  finger,  our  very  thoughts  and 
reasonings,  are  productive  of  waste  in  the  tissues  concerned. 

It  is  due  to  the  repair  by  the  machinist  that  the  machine  is  kept 
in  normal  running  order;  likewise  it  is  due  to  the  proper  absorption, 
assimilation,  and  elimination  of  foodstuffs  taken  into  our  own  econ- 
omies that  the  body  owes  its  normal  function  and  health. 

The  digested  products,  having  arrived  at  their  destination  in 
the  organs  and  tissues,  undergo  two  kinds  of  chemical  processes  in 
the  presence  of  oxygen  and  under  the  peculiar  activity  of  the  cells. 
(328) 


METABOLISM.  329 

The  one  is  anabolism,  or  upbuilding;  the  other  catdbolism,  or  de- 
struction. These  two  processes  are  diametrically  opposite  to  one 
another,  so  that  by  virtue  of  the  one  the  organism  increases  in  bulk; 
by  reason  of  the  other  its  bulk  is  diminished. 

By  reason  of  the  anabolic  processes  the  nonliving  materials  of 
the  food  are  converted  into  the  complex  molecules  of  the  living 
tissues,  where  they  are  stored  up  to  form  a  store  of  potential  energy. 
At  any  time  the  organism  is  capable  of  transforming  this  potential 
energy  into  kinetic,  which  is  usually  most  conspicuous  to  the  observer 
as  heat  and  motion. 

By  the  transformation  the  complex  tissues  are  broken  down  into 
excretory  products  whose  structure  is  simple.  The  waste-materials 
leave  the  cells  to  be  carried  by  the  lymphatics  into  the  blood-stream, 
ultimately  to  reach  the  exterior  of  the  body  as  excreta  or  as  compo- 
nents of  some  secretions. 

The  two  processes,  anabolism  and  catabolism,  taken  conjointly 
constitute  what  is  known  as  metabolism :  an  exchange  of  material. 

Normal  metabolism  thus  requires  the  ingestion  of  suitable  qual- 
ity and  quantity  of  food,  which  must  be  absorbed,  assimilated,  and 
stored  within  the  tissues.  In  the  latter  place  there  must  occur  the 
necessary  transformation  of  the  food  in  its  now  complex  form  into 
simpler  products  of  effete  nature,  evolving,  at  the  same  time,  those 
functions  and  activities  which  are  common  to  the  organism.  In 
short,  all  of  the  physiological  phenomena  demonstrable  in  the  econ- 
omy are  the  result,  either  directly  or  indirectly,  of  anabolic  or  cata- 
bolic  changes. 

Equilibrium  of  Metabolism. — By  this  term  is  meant  that,  ordi- 
narily, just  as  much  foodstuffs  are  stored  up  within  the  tissues  as 
effete  matters  and  excretions  find  egress  from  the  economy.  For  the 
organism  to  remain  normal  there  must  exist  a  balance  between  in- 
come and  output.  So  long  as  this  condition  lasts  the  body  maintains 
its  bulk,  while  at  the  same  time  it  is  capable  of  performing  its  neces- 
sary functions.  Should  this  equilibrium  be  disturbed,  there  will 
occur  marked  changes  dependent  upon  whether  anabolic  or  catabolic 
processes  are  in  the  ascendancy. 

Anabolic  Processes  become  visible  during  (1)  the  growth  of  the 
body  in  infancy  and  adolescence,  and  (2)  during  convalescence  from 
a  serious  and  debilitating  disease. 

Catabolic  Processes  become  evident  during  old  age  and  in  the 
course  of  malignant  diseases.  Catabolism  is  the  destruction  of  tis- 
sue, from  which  process  result  the  numerous  manifestations  of  life. 


330  PHYSIOLOGY. 

Catabolism  is  carried  on  by  means  of  different  chemical  forces : — 

1.  DUPLICATION:   that  is,  the  decomposition  of  an  organic  sub- 
stance into  two  or  more  products  whose  sum  represents  exactly  the 
primitive  substance. 

2.  DEHYDKATION. — This  is  a  particular  form  of  duplication  in 
which  one  of  the  products  is  water. 

3.  OXIDATION. — This  is  the  most  important  part  of  the  chemical 
processes.     By  this  means  the  decomposition  is  accomplished  with 
fixation  of  oxygen,  such  as  the  decomposition  of  albumin,  sugars, 
and  fats. 

4.  SYNTHESIS. — This  is  the  combination  of  two  or  more  sub- 
stances whereby  result  a  third,,  new  substance.     Syntheses  are  char- 
acteristic of  anabolism,  but  yet  they  do  occur  in  catabolism.     Thus, 
with  the  disintegration  of  the  tissue-elements  into  benzoic  acid  and 
glycocoll  there  follows  hippuric  acid;   urea  is  formed  from  carbonic 
acid  and  ammonia. 

THE  AIM  OF  ALIMENTATION. 

Alimentation  has  for  its  end  (1)  to  furnish  materials  for  catab- 
olism  and  (2)  to  furnish  suitable  products  for  anabolism.  That  is, 
to  replace  and  rejuvenate  the  organized  substances  which  are  de- 
stroyed in  the  former  process. 

To  know  what  are  the  foods  which  the  body  needs,  it  becomes 
necessary  to  study  the  substances  which  undergo  anabolism  and 
catabolism.  It  is  these  substances  which  must  enter  into  our  daily 
nourishment.  These  two  processes  ensue  in  all  of  the  substances, 
without  any  exception,  which  compose  the  organism.  Hence,  all 
the  principles  of  which  the  economy  is  composed  are  indispensable  in 
food :  water,  proteids,  fat,  carbohydrates,  and  salts. 

Foods. — Each  one  of  these  principles  taken  in  an  isolated  man- 
ner is  not  a  complete  food,  since  it  is  not  able  to  replace  its  neighbor. 
Thus,  water  is  as  necessary  a  food  as  is  proteid,  but  yet  neither  is  a 
complete  food. 

A  food  is  any  product  which  is  capable  of  being  transformed  into 
a  proximate  principle  of  the  organism,  or  capable  of  at  least  dimin- 
ishing or  preventing  the  destruction  of  this  principle.  Hence,  a 
complete  food  is  the  sum  of  the  food-products  capable  of  preserving 
or  augmenting  the  sum  of  the  proximate  principles  of  which  the 
organism  is  composed. 

The  fundamental  principles  which  enter  into  the  chemical  com- 
position of  the  human  body — water,  proteids,  fats,  carbohydrates, 


METABOLISM.  331 

and  salts — are  in  themselves  composed  of  simple  elements :  0.,  H,  C, 
S,  X,  P,  Cl,  K,  Xa,  Ca,  Mg,  Fe,  silicon,  and  fluorin. 

Will  these  simple  elements,  upon  ingestion,  become  converted 
into  complex  principles  and  so  constitute  foods  ? 

They  will  in  the  case  of  the  plant,  for  it  is  able  to  form  a  com- 
plex frame  by  the  aid  of  simple  elements.  The  plant  is  a  synthetic 
laboratory  of  chemistry.  But  this  is  not  true  of  the  animal  organiza- 
tion. The  latter  is  incapable  of  anabolism  and  life  except  by  the 
aid  of  complex  food-combinations  such  as  have  been  formed  by  the 
plant.  Contrary  to  the  plant,  the  animal  is  a  laboratory  of  analytical 
chemistry.  The  animal  can  only  form  by  synthesis  combinations  of  a 
low  degree,  as  water,  benzoic  acid,  and  ammonia,  which  cannot  be 
built  up  in  the  animal.  But  the  plant  can  take  H,  0,  C02,  and  N, 
and  from  them  make  complex  and  elevated  combinations. 

BALANCE  OF  NUTRITIVE  EXCHANGE. 

To  ascertain  the  balance  of  nutritive  exchange,  a  comparison 
is  made  between  the  ingesta  and  egesta:  between  the  gains  and 
losses.  The  ingesta  consist  of  food  and  oxygen;  the  egesta  of 
various  excreta  and  of  the  carbon  dioxide  and  water  lost  by  the  lungs 
and  skin.  When  the  ingesta  equal  the  egesta  and  the  organism  neither 
gains  nor  loses  weight,  there  is  a  complete  nutritive  equilibrium. 

A  balance  of  water  is  made  by  giving,  upon  the  one  side,  the  quan- 
tity of  water  ingested  by  the  foods  and  drinks;  upon  the  other,  the 
quantity  of  water  eliminated  by  the  stools,  urine,  skin,  and  lungs. 
As  the  hydrogen  contained  in  the  food  is  oxidized  and  transformed 
into  water,  it  is  evident  that  in  a  state  of  equilibrium  the  quantity 
of  water  eliminated  will  be  much  greater  than  that  ingested.  By 
comparing  the  water  ingested  with  the  water  egested,  it  is  found  how 
much  oxygen  serves  to  burn  the  hydrogen. 

Definite  enough  information  is  obtained  regarding  the  balance 
of  metabolism  if  the  nitrogen  and  carbon  only  are  determined  in  the 
ingesta  and  egesta. 

The  balance  of  proteid  is  made  by  a  comparison  of  the  nitrogen 
ingested  with  that  egested,  for  the  amount  of  nitrogen  permits  us  to 
know  the  quantity  of  proteid,  since  100  parts  of  proteid  contain  16 
parts  of  nitrogen.  The  nitrogen  eliminated  is  found  in  the  urine. 

Nearly  all  of  the  proteid  that  is  destroyed  is  found  in  the  form 
of  urea,  uric  acid,  creatinin,  and  hippuric  acid  in  the  urine.  There 
is  also  found  in  the  stools  proteid  which  has  not  been  digested  or 
absorbed  along  the  digestive  tract.  A  part  of  the  nitrogen  is  elinii- 


332  PHYSIOLOGY. 

nated  by  the  desquamation  of  hairs,  nails,  and  epidermis.  But  it 
usually  suffices  to  determine  the  amount  of  nitrogen  in  the  stools 
and  urine. 

If,  in  making  up  the  balance,  it  be  found  that  the  ingesta  have 
more  than  equaled  the  egesta,  it  is  concluded  that  there  has  been  an 
anabolism  of  nitrogen.  On  the  other  hand,  should  the  egesta  contain 
more  nitrogen  than  the  ingesta,  then  there  has  been  a  catabolism  of 
proteid.  Should  the  income  and  output  be  equal,  it  is  concluded  that 
there  is  a  state  of  nitrogenous  equilibrium. 

The  carbon  contained  in  the  foods  and  organized  tissues  and 
which  is  destroyed  by  catabolic  phenomena  is  eliminated  by  the  skin 
and  lungs  under  the  form  of  C02,  by  the  urine  and  stools  under  the 
form  of  carbonated  organic  compounds.  From  the  comparisons  of 
the  ingesta  and  egesta  it  is  ascertained  whether  there  be  carbon  anab- 
olism, catabolism,  or  equilibrium. 

The  proteids,  fats,  and  carbohydrates  all  contain  carbon;  so  that 
if  there  be  a  gain  or  loss  of  carbon  it  may  be  from  the  proteids,  fats, 
and  carbohydrates.  To  arrive  at  some  solution,  it  becomes  necessary 
to  calculate  the  quantity  of  nitrogen  eliminated.  Every  hundred 
parts  of  proteid  contain  53.6  parts  of  carbon  and  16  parts  of  nitro- 
gen. If  it  be  known  how  much  proteid  be  destroyed,  nothing  is 
easier  than  to  calculate  the  quantity  of  carbon  which  belongs  to  it. 
The  remaining  carbon  that  is  eliminated  must  belong  to  the  fats  and 
carbohydrates. 

All  of  the  carbohydrates  ingested,  except  those  stored  up  as 
glycogen,  are  burned  up  in  the  metabolism  of  the  tissues  and  their 
carbon  found  in  the  excreta.  Hence,  by  calculating  the  quantity  of 
carbon- which  is  found  in  the  ingested  carbohydrates,  one  finds  what 
quantity  of  carbon  eliminated  belongs  to  the  decomposition  of  the 
carbohydrates.  If  there  be  an  excess  of  carbon  it  must  come  from 
the  fats,  since  the  latter  contain,  as  a  mean,  76.5  per  cent,  of  carbon. 
By  multiplying  the  surplus  of  carbon  by  1.3,  there  is  found  the 
quantity  of  fat  which  is  gained  .or  lost. 

EFFECTS  OF  STARVATION  UPON  THE  DESTRUCTION  OF 
PROTEID. 

The  influence  of  starvation  upon  the  catabolism  of  the  proteids 
has  been  studied  upon  animals  and  in  man.  During  starvation  the' 
organized  proteid  continues  to  be  destroyed  and  death  ensues  more 
or  less  quickly.  The  loss  of  proteid  is  greater  on  the  first  day,  and 
is  in  proportion  as  the  food  has  been  rich  in  proteid  and  the  animal 


METABOLISM.  333 

lias  drawn  from  and  stored  up  a  large  quantity  from  trie  circulation. 
The  more  fat  that  an  animal  has,  the  less  proteid  is  destroyed.  Dur- 
ing starvation  the  body-fat  is  rapidly  diminished.  The  fat-cells  give 
up  their  fat,  becoming  smaller,  but  yet  retaining  their  envelopes. 
The  reabsorbed  fat  is  thus  capable  of  taking  the  place  of  a  diet  for 
a  considerable  length  of  time. 

Work. — The  researches  of  many  observers  have  demonstrated 
that  muscular  work,  however  exaggerated  it  may  be,  does  not  influ- 
ence the  destruction  of  proteids,  except  to  a  small  extent.  Varia- 
tions of  the  temperature  of  the  air  do  not  influence  the  destruction  of 
proteids.  Should  there  be  fever,  the  destruction  of  proteid  and  fat 
increases. 

METABOLISM. 

Catabolism  varies  according  to  the  age  and  weight  of  the  animal; 
the  younger  and  lighter  the  animal,  the  greater  is  the  relative  de- 
struction of  proteid. 

Peptones  and  albumoses  have  about  the  same  caloric  and  nutri- 
tive value  as  the  proteids.  Most  of,  if  not  all,  the  proteids  contain 
sulphur,  and  the  nucleo-proteids  contain  phosphorus.  An  increase 
of  sulphates  in  the  urine  indicates  proteid  metabolism. 

As  agents  to  spare  proteid  metabolism,  gelatin  ranks  first,  then 
carbohydrates,  and  next  fats.  Gelatin,  however,  cannot  be  built  up 
into  tissue,  nor  even  into  gelatin. 

Fats. 

The  quantity  of  fats  in  healthy  persons  may  vary  greatl}r:  from 
2.5  to  23  per  cent.  Fats  are  encountered  in  two  forms  in  the  organ- 
ism: (a)  as  an  emulsion  in  the  nutritive  fluids;  (b)  in  drops  in  small 
particular  cells  or  in  the  interior  of  tissue-cells.  While  in  the  emul- 
sion state  the  fats  are  in  circulation,,  in  the  second  state  they  are  at 
rest.  The  combustion  of  fats  produces  water  and  C02. 

Origin  of  Fats. — Fats  are  deposited  within  the  body  from  the 
fats,  proteids,  and  carbohydrates  absorbed  in  the  digestion  of  food. 
Proteids  may  be  decomposed  to  produce  fat.  Thus,  if  a  lean  animal 
be  poisoned  by  phosphorus,  large  quantities  of  fat  will  be  found  in 
its  liver.  The  carbohydrates  form  one  of  the  principal  sources  of  fat. 

While  muscular  exercise  has  hardly  any  influence  upon  proteid, 
it  is  not  so  with  fats.  The  latter  are  rapidly  used  up.  Hence,  a 
man  who  works  has  need  of  more  fat  than  one  who  pursues  a  seden- 
tary life. 


334  PHYSIOLOGY. 

Carbohydrates. 

The  carbohydrates  are  found  in  small  proportion  in  flesh-foods, 
as  glycogen,  and  in  milk  in  the  form  of  lactose.  By  far  the  greater 
proportions  of  carbohydrates  are  obtained  from  the  vegetable  king- 
dom. In  vegetable  foods  they  occur  as  starches  and  sugars. 

An  animal  that  is  fed  upon  carbohydrates  exclusively  dies  of 
starvation  on  account  of  want  of  proteid.  The  saving  of  proteid 
increases  proportionately  with  the  quantity  of  carbohydrates  in- 
gested. This  is  an  important  fact,  since  the  digestive  juices  are 
capable  of  digesting  them  in  large  quantities. 

The  fatigue  of  muscle  is  slowed  by  the  use  of  sugar.  Dr.  Lee 
gave  animals  phloridzin  for  four  days,  which  sweeps  the  greater  part 
of  the  carbohydrate  material,  or  glycogen,  out  of  the  muscles.  Then 
he  irritated  the  tibialis  anticus,  and,  while  it  gave  1000  contractions 
per  minute  on  electrical  stimulation  normally,  after  the  removal  of 
glycogen  by  the  phloridzin  the  contractions  were  only  from  200  to 
400  per  minute.  These  experiments  proved  that  carbohydrates  as- 
sisted the  muscle  in  its  contraction.  He  made  another  series  of 
experiments  upon  the  muscles  which  had  their  glycogen  removed  by 
phloridzin,  and  then  gave  50  grams  of  dextrose.  Then  electrical 
irritations  were  used  on  the  muscles,  which  gave  650  contractions  per 
minute.  Here  the  glucose  restored  the  muscle. 

Water. 

Among  the  inorganic  compounds,  the  most  important,  without 
exception,  is  water.  It  is  even  more  important  than  proteid  and  fat, 
since  it  forms  about  three-fifths  of  the  weight  of  the  body. 

Water  has  an  important  function  within  the  organism.  When 
proteid  is  insufficient,  water  accumulates  in  the  tissues.  Among  the 
poorer  classes,  whose  nourishment  is  insufficient,  infectious  diseases 
flourish,  since  their  nutritive  liquids  are  excellent  media  for  the 
cultivation  of  micro-organisms. 

Excess  of  water  causes  an  augmentation  of  urea;  hence  the 
success  of  mineral  waters  in  Bright^  disease.  This  increase  of  urea 
is  due  to  the  abundant  washing  out  of  the  retarded  metabolic  acts 
through  the  kidneys. 

Salts. 

There  is  not  any  liquid  nor  any  tissue  which  does  not  produce 
an  ash  upon  calcination.  The  inorganic  salts  are  either  in  solution 


METABOLISM.  335 

or  combined  with  organic  substances,  notably  proteid.  The  combina- 
tion of  the  various  needful  salts  with  protoplasm,  the  substratum  of 
life,  is  of  the  highest  importance.  Of  the  various  salts  found  within 
the  tissues,  sodium  chloride  is  the  most  important. 

Lime  and  Magnesia  Salts. — The  alkaline  earths,  if  in  too  great 
quantity,  may  precipitate  to  form  hepatic  calculi. 

The  phosphate  of  lime  forms  the  greater  part  of  bone.  Bone 
depends  upon  the  salts  of  lime  found  in  the  food. 

Lime  occurs  in  large  amount  in  milk.  The  only  other  food 
which  has  the  same  amount  as  milk  is  the  yelk  of  egg.  This  latter 
should  be  given  to  children  when  inilk  is  not  at  hand  or  not  readily 
digested.  Withholding  lime  is  favorable  to  the  production  of  rickets. 
Calcium  is  excreted  with  the  succus  entericus  chiefly. 

Animals  from  whose  food  the  salts  have  been  extracted  very 
frequently  die  more  rapidly  than  animals  from  whom  food  has  been 
entirely  withheld.  There  is  caused  a  train  of  symptoms  indicating  a 
disturbance  of  the  central  nervous  apparatus  and  the  digestive  sys- 
tem. This  untoward  result  is  due  to  chronic  sulphuric-acid  poisoning 
from  oxidation  of  the  sulphur  of  the  proteids. 

Now,  the  bases  in  the  blood  which  neutralize  are  the  sodium 
carbonate  and  sodium  phosphate,  and  it  has  been  estimated  that  the 
amount  of  this  alkaline  reacting  alkali  or  native  alkali  in  the  entire 
body  is  equivalent  to  60  grams  of  sodium  hydroxide  (NaOH).  This 
amount  of  alkali  is  so  small  that  it  would  be  quickly  exhausted  by  a 
persistent  acid  intoxication  with  a  persistent  formation  of  only  small 
amounts  of  acid.  Certain  diabetic  patients  pass  daily  for  long  periods 
a  large  amount  of  acids  which  are  excreted  by  the  urine  in  combina- 
tion with  bases,  it  being  understood  that  the  urine  does  not  contain 
free  acid.  As  the  native  alkali  of  the  body  is  not  sufficient  to  neu- 
tralize so  much  acid,  it  is  necessary  that  there  must  be  another  and 
more  enduring  source  of  alkali  than  the  native.  For  this  ammonia  is 
generated  by  proteid  metabolism  of  the  cells  and  especially  of  meat. 
The  acids  in  diabetes  are  the  aceto-acetic  and  the  oxybutyric,  which 
can  be  detected  in  the  urine.  Acetone  is  also  present  in  the  urine  of 
severely  diseased  diabetics.1 

Iron. — Such  compounds  of  iron  as  are  contained  in  nuclein  as 
found  in  the  yelk  of  egg  have  been  termed  by  Bunge  hcematogens.  In 
the  chick  the  developing  red  corpuscles  obtain  their  iron  from  it. 
Iron  is  absorbed  through  the  duodenum  and  excreted  mainly  through 


1Herter:    "Chemical  Pathology,"  1902. 


336 


PHYSIOLOGY. 


the  mucous  membrane  of  the  colon.  Inorganic  and  organic  combina- 
tions of  iron  are  absorbed.  Iron  is  deposited  in  lymph-ganglia,  spleen, 
and  liver. 

Diet. 

The  diet  of  a  healthy  man  has  for  its  aim  not  only  to  cover  any 
deficit  without  catabolism  ceasing  and  of  maintaining  the  system  in 
a  state  of  integrity  indispensable  to  its  physiological  functions,  but 
also  to  furnish  to  the  organism  a  certain  food-reserve  so  that  the 
body  will  not  lose  its  own  proper  tissue.  To  ascertain  exactly  the 
quantity  of  nourishment  necessary  to  keep  the  body-weight  the  same 
it  is  necessary  to  have  recourse  to  experiments. 

Example  of  a  Metabolism  Investigation. 

I  have  selected  as  an  example  one  given  by  Beddard.1 

It  is  desired  to  know  whether  a  diet  containing  125  grams  of 

proteid,  50  grams  of  fat,  and  500  grams  of  carbohydrate  is  sufficient 

for  a  man  doing  a  moderate  amount  of  work. 


INTAKE. 


CALORIES. 


Proteid  .    . 

Carbohydrate 

Fat 


62  grams. 
200       " 
_38       " 
300       u 


20  grams. 

00 

00 

20  grams. 


51-2.5 
2050.0 

465.0 
3027.5 


OUTPUT. 


In  urine  . 
In  faeces  . 
In  breath 


11  grams   (16.5X0.67) 
5       " 
254       " 
270       " 


16.5  grams. 

1.0  gram. 

0.0 

17.5  grams. 


Eetained  in  body,  30  grams  of  carbon  and  2.5  grams  of  nitrogen. 
This  amount  of  nitrogen  represents  2.5  X  6.25  =  15.6  grams  proteid, 
or  75  grams  of  muscle.  Now,  this  amount  of  proteid  will  account  for 
8.25  grams  of  carbon;  so  that  30  —  8.25  =  21.75  grams  of  carbon 


1W  Practical  Physiology." 


METABOLISM.  337 

represents  21.75  X  1.3  =  28.3  grains  of  fat.  On  this  diet,  therefore, 
the  subject  retains  in  his  tissues  15.6  grams  proteid  and  28.3  grams 
fat  per  diem. 

To  express  this  result  in  terms  of  energy  liberated,  we  know 

that  3027.5  calories  were  supplied,  and  that  all  these  have  been  used 

except  15.6  X  4.1  =  64  retained  as  proteid  and  28.3  X  9.3  =  263.2 

retained  as  fat,  or,  in  toto,  327.2  C.     We  find,  therefore,  that  3027.5 

-  327.2  =  2700  C.  have  been  required. 

One  gram  of  fat  when  burned  produces  9.5  Calories. 

One  gram  of  proteid  when  burned  produces  about  4.1  Calories. 

One  gram  of  carbohydrate  when  burned  produces  4.1  Calories. 

One  gram  of  alcohol  when  burned  produces  7  Calories. 

One  large  Calorie  equals  1000  small  calories.  The  large  Calorie 
is  written  with  a  capital  C ;  the  small  calories  with  a  small  c. 

Obesity  is  produced  by  all  the  causes  which  slow  the  organic  oxi- 
dations, as  sedentary  life,  absence  of  work  or  locomotion,  and  insuf- 
ficiency of  air  and  light.  Predisposing  causes  are  heredity,  anaemia, 
and  sexual  influences. 

Development  and  Growth. 

When  the  anabolic  and  catabolic  processes  are  balanced  in  adult 
life,  the  body  remains  the  same  in  weight. 

The  progressive  development  of  the  body  in  height  is  made  in  an 
uneven  manner,  dependent  upon  different  ages.  In  the  first  year  the 
growth  is  about  twenty  centimeters.  From  the  fourth  and  fifth  years 
up  to  puberty  there  is  each  year  an  increase  of  one  twenty-first  of  the 
total  height. 

On  the  contrary,  the  development  in  thickness  and  breadth  is 
slower  during  the  first  years  than  at  puberty;  toward  the  fortieth 
and  fiftieth  years  it  attains  its  maximum. 

The  tissues  of  the  organs  may  increase  in  two  ways :  by  increase 
in  volume  of  existing  elements  or  by  the  multiplication  of  new  cells. 

Bones  present  certain  physiological  properties  of  great  interest, 
for  they  grow  in  both  length  and  thickness.  The  increase  in  length 
is  at  each  end  of  the  bone  at  the  junction  of  the  epiphysis  with  the 
diaphysis.  The  increase  in  thickness  is  made  by  means  of  the  peri- 
osteum adding  new  layers  of  bone  on  the  surface. 


CHAPTER  X. 

ANIMAL  HEAT. 

INORGANIC  bodies  have  a  constant  tendency,  either  by  losing  or 
gaining  heat,  to  adapt  themselves  to  the  temperature  of  surrounding 
media  or  objects.  They  may  be  artificially  cooled  or  artificially 
heated  to  all  possible  degrees. 

Living  plants  and  animals  also  receive  and  give  off  heat  physic- 
ally; but,  in  addition,,  they  possess  a  common  power  of  resisting 
external  temperatures.  With  plants  this  power  is  very  feeble  in 
degree ;  with  animals  it  is  more  marked.  Among  the  higher  animals, 
especially,  is  there  an  inherent  power  to  maintain  a  temperature  that 
differs  from  that  of  the  surrounding  media.  Since  living  animals, 
like  dead  ones  and  inorganic  bodies,  exhibit  the  same  physical  phe- 
nomena of  absorption,  conduction,  and  radiation  of  heat,  they  un- 
dergo constant  changes;  these  are  usually  in  the  direction  of  loss  of 
heat.  Hence  there  must  exist  within  them  a  power  of  constant 
renewal  or  production  of  heat  to  take  the  place  of  that  lost.  This 
function  of  producing  heat  is  universal  with  the  warm-blooded  ani- 
mals, and  all  of  the  processes  of  life  are  influenced  by  it.  Certainly 
the  higher  animals  have  within  their  bodies  not  only  some  means  to 
produce  heat,  but  some  mechanism  whereby  the  production  and  loss 
are  regulated.  Thus,  though  the  temperature  of  the  surrounding 
atmosphere  be  very  high,  as  in  midsummer,  or  very  low,  as  in  mid- 
winter, yet  the  standard  temperature  of  the  animal's  body  remains 
uniform  and  constant.  The  energy  necessary  to  accomplish  this  is 
known  as  animal  heat. 

Physical  Heat. — Heat  is  a  form  of  energy  exhibited  by  matter. 
We  cannot  create  or  destroy  either. 

Energy  is  the  power  to  do  work.  Any  agent  that  is  capable  of 
doing  work  is  said  to  possess  this  property.  The  quantity  of  energy 
that  it  possesses  is  measured  by  the  amount  of  work  it  can  do.  When 
a  body  is  hot  it  possesses  a  store  of  energy  which  may  be  exhibited  by 
the  heated  matter. 

Energy  is  known  in  two  forms:  1.  The  energy  possessed  by  a  body 
in  consequence  of  its  velocity  is  known  as  energy  of  motion,  or  kinetic 
energy.  The  body  in  motion  which  has  this  kinetic  energy  communi- 
(338) 


ANIMAL  HEAT.  339 

cates  it  to  some  other  body  during  the  process  of  bringing  it  to  rest. 
This  is  the  fundamental  form  of  energy. 

2.  The  other  form  of  energy  which  a  body  may  have  depends  not 
upon  its  own  state,  but  upon  its  position  with  respect  to  other  bodies. 
It  is  the  energy  possessed  by  a  mass  in  consequence  of  its  having 
been  raised  from  the  ground.  Potential  energy  can  exist  in  a  body 
all  of  whose  parts  are  at  rest. 

Radiant  heat  is  one  and  the  same  thing  as  that  which  we  call 
light.  When  detected  by  the  thermometer  or  by  the  sensation  of  heat, 
it  is  called  radiant  heat. 

When  equal  weights  of  quicksilver  and  water  are  mixed  together, 
the  resulting  temperature  is  not  the  mean  of  the  temperature  of  the 
ingredients.  The  effect  of  the  same  quantity  of  heat  in  raising  the 
temperature  of  two  bodies  depends  not  only  on  the  amount  of  matter 
in  the  bodies,  but  also  upon  the  kind  of  matter  of  which  each  is 
formed.  This  is  called  capacity  of  heat,  or  specific  heat. 

The  capacity  of  a  body  for  heat  is  the  number  of  units  required 

to  raise  that  body  one  degree  of  temperature.    The  specific  heat  of 

'  a  body  is  the  ratio  of  the  quantity  of  heat  required  to  raise  that  body 

one  degree  to  the  quantity  required  to  raise  an  equal  weight  of  water 

one  degree. 

Latent  heat  is  the  quantity  of  heat  that  must  be  communicated 
to  the  body  in  a  given  state  to  convert  it  into  another  state  without 
changing  the  temperature. 

The  higher  the  temperature  of  a  body,  the  greater  is  its  radia- 
tion. When  the  temperature  of  bodies  is  unequal,  the  hotter  bodies 
will  emit  more  heat  by  radiation  than  they  receive  from  the  colder. 
Therefore,  on  the  whole,  heat  will  be  lost  by  hotter  and  gained  by 
colder  bodies  until  thermal  equilibrium  is  attained. 

The  cause  of  heat  is  popularly  explained  to-day  by  what  is  known 
as  the  "undulatory  theory."  According  to  its  doctrines,  the  heat  of 
a  body  is  caused  by  an  extremely  rapid  oscillating  or  vibratory  motion 
of  its  molecules.  The  hottest  bodies  are  those  in  which  the  vibra- 
tions have  both  the  greatest  velocity  and  the  greatest  amplitude. 
Hence,  heat  is  not  a  substance,  but  a  condition  of  matter.  It  is  a 
condition  which  can  be  transferred  from  one  body  to  another.  When 
a  heated  body  is  placed  in  contact  with  a  cooler  one,  the  former  gives 
more  molecular  motion  than  it  receives;  but  the  loss  of  the  former 
is  the  equivalent  of  gain  of  the  latter. 

Animal  Heat. — Within  the  organs  of  the  human  body,  as  well  as 
those  of  all  animals,  processes  of  oxidation  are  continually  going  on. 


340  PHYSIOLOGY. 

Oxygen  passes  through  the  lungs  into  the  blood  to  be  thus  carried  to 
all  parts  of  the  body.  In  like  manner  the  oxidizable  bodies,  which 
are  principally  foods,  pass  by  the  processes  of  digestion  into  the 
blood  finally  to  reach  every  part  of  the  body.  The  gases,  liquids, 
and  solids  which  enter  the  body  are  loaded  with  energy.  These 
various  bodies  are  intimately  concerned  in  the  different  chemical 
processes  which  sum  up  metabolism:  that  is,  those  phenomena 
whereby  living  organisms  are  capable  of  incorporating  substances 
obtained  from  their  food  into  their  tissues.  Metabolism  is  also  con- 
cerned in  the  formation  of  a  store  of  potential  energy  which  may 
readily  be  transformed  into  kinetic  energy,  as  manifested  in  muscular 
work  and  heat.  Within  the  body  the  assimilable  substances  undergo 
many  chemical  changes,  and  finally  leave  it  in  forms  quite  different 
from  those  entering  it.  The  oxygen  inspired  combines  mainly  with 
carbon  and  hydrogen  to  form  carbon  anhydride  and  water,  while  the 
more  complicated  compounds  are  reduced  to  simple  bodies,  to  be 
excreted  as  such.  In  the  process  of  disintegrating  these  compounds 
—in  fact,  in  catabolism  in  general — one  of  the  most  important  re- 
sults is  the  production  of  heat.  The  energy  enters  the  body  as  poten- 
tial energy  stored  up  in  the  food.  By  chemical  processes  it  becomes 
evolved  into  kinetic  energy  and  heat.  Animal  heat  is  the  accompani- 
ment of  the  formation  of  carbonic  acid,  urea,  and  other  excreted 
products.  According  to  our  theory  of  heat,  the  animal  heat  due  to 
metabolic  processes  must  represent  to  us  vibrations  of  the  corporeal 
atoms. 

Other  Sources. — Boughly  speaking,  the  muscles  constitute  about 
one-half  of  the  whole  mass  of  the  body,  the  bones  the  other  half.  As 
but  little  oxidation  occurs  in  the  bones,  the  muscles  must  be  the 
chief  seat  of  heat  production.  Muscular  exercise  greatly  increases 
the  metabolism  and  the  C02  excreted,  but  there  is  an  accompanying 
increase  in  heat  production.  In  health  the  muscles  yield  four-fifths 
of  the  body-heat. 

The  secreting  glands  are  known  to  be  centers  of  thermogenesis 
as  well.  The  alimentary  canal  during  digestion  and  also  the  liver  are 
very  marked  sources.  In  fact,  the  blood  in  the  hepatic  veins  is  the 
warmest  part  of  the  body.  The  function  of  the  muscles,  tendons, 
ligaments,  and  bones  is  not  a  very  slight  source  of  warmth. 

It  must  be  borne  in  mind  by  the  student  that  the  processes  of 
oxidation  are  concerned  not  only  in  the  combustion  of  the  digested 
foodstuffs,  but  a.lso  of  the  cells  of  the  body.  It  is  the  oxidation  of 
their  protoplasm  that  evolves  warmth. 


ANIMAL  HEAT.  341 

Warm-blooded  and  Cold-blooded  Animals. — Depending  upon  the 
relationship  of  the  temperature  of  the  animal's  body  and  that  of  the 
enveloping  media  there  are  two  great  classes:  liomotliermal  and 
poikilotliermal. 

The  liomotliermal,  or  warm-blooded,  animals  include  the  higher 
orders  of  the  animal  kingdom,  in  whom  the  temperature  remains 
fairly  constant  despite  variations  in  temperature  of  the  enveloping 
media.  The  temperature  of  this  class  of  animals  is  high,  but  uni- 
form. Should  homothermal  animals  remain  a  considerable  length  of 
time  in  a  cold  medium,  their  heat-producing  organs  become  more  ac- 
tive in  order  to  compensate  for  that  lost  rapidly  by  radiation.  When 
they  remain  in  very  warm  media,  heat  production  is  diminished. 

Poikilothemnal,  or  cold-blooded,  animals  constitute  that  class  of 
lower  animals  whose  temperature  bears  a  very  intimate  relationship 
and  is  dependent  upon  that  of  the  enveloping  media.  Their  tem- 
perature is  thus  subject  to  very  considerable  variations,  although  it 
is  always  slightly  above  that  of  its  surroundings.  When  the  tempera- 
ture of  the  surrounding  medium  is  raised,  the  amount  of  heat  pro- 
duced within  poikilothermal  animals  is  increased.  Inversely,  when 
the  enveloping  temperature  falls,  the  heat  production  within  the  ani- 
mal is  diminished.  This  class  includes  reptiles,  amphibians,  fish,  and 
most  invertebrates. 

However,  the  line  of  demarcation  between  the  two  classes  of 
animals  is  not  a  very  clear  and  decisive  one.  For  there  are  some 
animals,  as  the  bat  and  dormouse,  which  seem  to  be  intermediary. 
In  summertime  they  possess  a  high  temperature  that  is  independent 
of  their  surroundings ;  in  winter  they  become  dormant  and  hibernate. 
While  in  this  latter  condition  their  temperature  varies  with  that  of 
the  enveloping  medium. 

Temperature  of  Man. — Although  the  blood  in  circulation  tends 
to  distribute  the  heat  of  the  body  uniformly,  yet  there  are  found 
slight  variations  in  different  regions.  These  regions  are  principally 
upon  the  surface,  where  exposure  is  such  that  the  leveling  function 
of  the  blood  is  hindered.  The  mean,  daily  temperature  of  a  healthy 
man  varies  between  98°  and  99°  F.  In  the  rectum  it  is  98.96°  F.;  in 
the  axilla,  98.45°  F.;  in  the  mouth,  98.36°  F.  These  figures  repre- 
sent the  averages  obtained  from  various  observations,  but  they,  too, 
are  subject  to  many  variations  from  exercise,  rapid  respiration,  food 
within  the  alimentary  tract,  etc. 

From  frequent  observations  and  numerous  tables  it  will  be 
found  that  the  mean  rectal  temperature  of  oilier  mammals  is,  for  the 


342  PHYSIOLOGY. 

most  part,  higher  than  that  of  man.  In  the  case  with  birds,  the 
temperature  averages  from  two  to  three  degrees  higher  than  that  of 
mammals.  In  securing  these  observations  it  is  always  necessary  that 
the  animal  should  not  struggle  either  before  insertion  or  during  the 
time  that  the  thermometer  is  in  position.  A  faulty  reading  of  as 
much  as  three  degrees  may  occur  when  the  animal  struggles  or  has 
been  previously  chased. 

Hibernation. — Many  animals  regularly  at  the  approach  of  cold 
weather  gradually  lose  their  activities  until  they  apparently  have 
lost  all  of  their  functions  and  are  dormant.  Such  a  state  is  known 
as  hibernation.  The  temperature  of  the  animaFs  body  is  but  a  trifle 
above  that  of  the  surrounding  atmosphere.  The  respirations  are 
greatly  decreased  in  number,  while  the  rhythm  is  of  the  Cheyne- 
Stokes  type.  The  heart's  action  in  point  of  force  and  frequency  is 
much  reduced  during  hibernation.  Animals  whose  hearts  during 
active  life  beat  one  hundred  or  more  now  register  but  fourteen  or 
sixteen  per  minute.  The  digestive  powers  are  at  a  very  low  ebb,  while 
as  to  its  nervous  sensibilities  the  animal  is  very  markedly  depressed. 

The  awakening  from  hibernation  is  a  most  interesting  phenom- 
enon in  so  far  as  the  rise  of  the  animaFs  temperature  is  very  sudden. 
So  sudden  is  the  rise  and  in  so  short  a  time  is  it  accomplished  that  it 
surpasses  the  most  rapid  rise  in  temperature  of  any  fever.  With 
proportionate  celerity  are  the  vital  functions  spurred  on  to  activity. 

Modifying  Influences. — Close  observation 'shows  that  there  occur 
slight  variations  in  man's  daily  temperature.  It  is  found  to  rise 
during  the  late  morning  and  afternoon;  to  fall  during  the  evening 
and  early  morning.  Because  of  differences  in  age  of  subjects,  modes 
of  living,  climate,  etc.,  observers  are  not  agreed  as  to  the  maximum 
and  minimum  temperatures.  However,  it  may  be  safe  to  say  that 
the  maximum  temperature  is  attained  about  from  3  to  5  o'clock  in 
the  afternoon,  while  the  minimum  is  registered  at  from  3  to  -5 
o'clock  in  the  morning.  The  range  of  difference  averages  about  1°  C. 

CAUSES. — Probably  the  two  most  important  causes  for  these  nor- 
mal variations  are  muscular  activity  and  food-ingestion.  It  is  during 
the  day  that  man,  as  a  rule,  is  most  active  and  it  is  then  that  he 
usually  replenishes  the  waste  of  his  body  by  the  consumption  of  a 
proper  amount  of  food.  Naturally  he  will  be  most  inactive  during 
the  night;  his  bodily  functions  will  be  depressed  at  that  time  so  that 
just  so  much  heat  will  be  generated  as  the  economy  needs. 

It  has  been  found  that  the  maximum  and  minimum  points  of 
temperature  in  man  can  be  inverted.  Thus,  if  a  man  change  his 


ANIMAL  HEAT.  343 

mode  of  life  so  that  he  continue  to  work,  for  a  considerable  length  of 
time  at  night  and  sleep  in  the  daytime,,  after  a  week's  time  there  will 
be  noted  a  gradual  change  toward  inversion.  It  is  well  to  note  also 
that  the  high  and  low  points  of  temperature  of  the  body  correspond 
to  those  times  when  the  external  temperature  is  high  and  low,  re- 
spectively. Radiation  may  thus  be  a  not  inconsiderable  factor. 

Age.  —  Just  before  birth  the  infant's  temperature  is  generally 
somewhat  higher  than  that  of  its  mother's  uterus.  After  birth  and 
during  the  first  few  weeks  the  temperature  remains  fairly  constant, 
but  still  a  little  high.  There  is  a  fall  of  one-tenth  or  two-tenths  from 
infancy  to  puberty;  a  like  amount  from  the  latter  period  to  middle 
life,  when  there  occurs  a  slight  rise. 

During  muscular  work  the  temperature  rises  rapidly,  but,  by 
reason  of  compensatory  measures,  the  loss  by  radiation  and  con- 
duction is  almost  proportionately  increased.  So  nearly  are  the  gen- 
eration and  loss  balanced  that  during  actual  work  there  is  registered 
but  a  rise  of  a  degree  and  a  fraction.  With  the  conclusion  of  the 
muscular  activity  the  temperature  very  rapidly  falls  to  normal. 
Mental  work  causes  a  rise  of  both  the  general  as  well  as  local  tem- 
perature of  the  brain  and  head.  The  increase  registered  is  usually 
about  0.1°  C.- 

Food  causes  a  very  slight  rise  in  temperature ;  sleep,  in  itself,  ha* 
no  effect.  Inactivity  is  a  very  marked  factor  in  producing  a  fall.  As 
inaction  is  very  prominent  during  sleep,  the  latter  has  been  erro- 
neously given  the  credit  for  causing  the  drop  in  temperature.  Lying 
perfectly  quiet  will  produce  identical  results.  Because  of  the  heat, 
the  inhabitants  of  tropical  countries  possess  a  slightly  higher  tem- 
perature. The  difference  is  less  than  1°  C. 

Extremes  of  Temperature. — During  excessively  hot  spells  in  sum- 
mertime when  the  temperature  of  the  enveloping  atmosphere  is  con- 
siderably above  that  of  the  normal  body-temperature,  it  is  remarkable 
to  find  that  the  temperature  of  the  body  has  not  been  raised  one 
degree.  This  result  is  mainly  accomplished  by  reason  of  the  heat 
extracted  from  the  body's  surface  during  evaporation. 

The  limit  of  extreme  cold  is  reached  when  the  tymph  within  the 
animal's  tissues  is  frozen.  Fishes  have  been  incased  within  ice  and 
then  found  completely  to  recover  upon  being  thawed  out  and  placed 
in  a  warmer  medium.  Normally,  the  range  of  temperature  in  a  man 
is  about  1°  C.  However,  drunkards  have  been  known,  after  exposure 
to  extreme  cold,  to  have  a  body-temperature  as  low  as  24°  C.  without 
fatality. 


344  PHYSIOLOGY. 

Cases  of  temperature  as  high  as  45°  C.  have  been  noted  and  yet 
recovery  has  taken  place.  Experimentally,  Bernard  found  that,  when 
the  internal  temperature  of  rabbits  was  raised  to  45°  C.,  they  died. 
According  to  his  view,  death  occurred  as  the  result  of  stoppage  of 
the  heart  from  the  hot,  circulating  blood,  causing  rigor  mortis  of  the 
musculature  of  this  organ. 

Temperature  of  the  Blood.  —  The  average  temperature  of  the 
blood  is  39°  C.,  but  there  are  found  numerous  variations  in  different 
regions.  The  blood  of  the  superficial  veins  is  cooler  than  that  of  the 
internal  veins,  due  to  prolonged  exposure  while  traversing  the  course 
of  the  former.  The  warmest  blood  of  the  body  is  that  of  the  hepatic 
veins.  The  blood  in  the  veins  is  cooler  than  the  blood  in  the  cor- 
responding arteries,  due  to  the  more  superficial  position  of  the 
former.  The  temperature  of  the  blood  of  the  left  heart  is  some- 
what lower  than  that  of  the  right.  This  has  been  explained  on  the 
ground  that  the  right  heart  is  in  closer  proximity  to  the  warm  liver ; 
also,  that  the  blood  going  to  the  left  heart  has  been  cooled  from 
its  passage  through  the  lungs  during  respiration. 

Estimation  of  Temperature. — Our  knowledge  as  to  difference  in 
degree  of  the  heat  of  the  same  or  different  bodies  is  gained  by  ther- 
mometry.  Thermometers  are  instruments  for  measuring  tempera- 
tures. Their  principle  is  based  upon  the  physical  phenomenon  of 
expansion  of  bodies  by  heat.  Liquids  are  best  suited  for  this  purpose. 
Mercury  and  alcohol  are  the  only  two  liquids  used. 

The  mercurial  thermometer  is  the  one  most  extensively  used.  It 
consists  of  a  capillary  glass  tube,  at  the  end  of  which  is  blown  the 
bulb.  Both  the  bulb  and  a  portion  of  the  tube  are  filled  with  mer- 
cury. The  expansion  of  the  mercury  is  registered  by  a  scale,  which  is 
graduated  either  upon  the  stem  itself  or  upon  a  frame  to  which  it  is 
attached.  On  the  Continent,  and  more  especially  in  France,  the  stem 
is  divided  into  one  hundred  parts,  or  degrees ;  this  division  is  known 
as  the  Centigrade  scale.  In  England,  in  Holland,  and  in  North  Amer- 
ica the  Fahrenheit  scale  is  used.  Its  stem  is  divided  into  two 
hundred  and  twelve  degrees  between  zero  and  the  boiling-point  of 
water. 

Estimation  of  Heat. — Calorimetry  is  the  measure  of  the  quantity 
of  heat  which  results  from  the  transformation  of  energy.  By  it  is- 
learned  the  amount  of  heat  possessed  by  any  body,  and  what  amount 
of  heat  the  latter  is  capable  of  producing.  Calorimetric  measurements 
are  expressed  in  thermal  units.  A  certain  quantity  of  heat  with  which 
all  other  quantities  are  compared  is  known  as  a  thermal,  or  heat,  unit. 


ANIMAL  HEAT. 


345 


A  thermal  unit  is  the  quantity  of  heat  required  to  raise  a  pound 
of  water  from  one  defined  temperature  to  another  defined  temperature. 
A  particular  thermal  unit  has  been  called  by  some  authors  a  Calorie. 
It  is  the  quantity  of  heat  necessary  to  raise  a  kilogram  (2.2  pounds) 
of  water  1°  C.  An  English  heat  unit  is  the  quantity  of  heat  re- 
quired to  elevate  one  pound  of  water  1°  F.  One  Calorie  equals 
3.96  English  heat  units.  In  Germany  scientists  frequently  use  the 
word  calorie,  but  mean  the  gram-calorie.  It  represents  the  quantity 
of  heat  that  is  required  to  elevate  the  temperature  of  1  gram  of 
water  1°  C. 

The  whole  science  of  animal  heat  is  founded  upon  thermometry 
and  calorimetry,  as  well  as  the  indirect  method  of  calculating  the 
quantity  of  heat  produced  from  the  quantity  of  nutritive  materials 
that  have  been  consumed.  There  are  various  types  of  calorimeters 


Fig.  77. — Human  Calorimeter. 

in  existence,  but  it  has  only  been  within  the  past  few  years  that  re- 
sults at  all  exact  have  been  attained. 

,  The  calorimeter  employed  by  the  author  in  his  laboratory  ex- 
periments is  constructed  as  follows:  It  is  composed  of  two  cylinders 
of  galvanized  iron — one  smaller  than  the  other  and  inclosed  within 
the  larger.  The  space  in  which  the  man  lies  upon  a  mattress  is  six 
feet  long  and  two  feet  in  diameter.  Air  is  conveyed  to  him  through 
the  tube  (H)  which  traverses  the  whole  length  of  the  apparatus  to 
enter  the  hollow  tube  of  lead  at  F;  it  finally  emerges  at  B,  after 
having  given  off  its  heat  to  the  water  between  the  two  cylinders. 
The  meter  (M )  is  run  by  the  water-wheel  (N),  which  aspirates  the 
air  through  the  entire  apparatus  by  means  of  a  hose  (R)  connecting  it 
with  the  lead  tube  at  B. 


346  PHYSIOLOGY. 

The  space  between  the  cylinders  is  filled  with  about  48i  pounds 
of  water.  This  water  is  kept  thoroughly  mixed  by  means  of  the  agi- 
tator (0),  which  has  two  arms.  The  arms  are  pushing  the  water 
back  and  forth  thirty  times  a  minute,  the  motion  being  caused  by  the 
electrical  motor  (X),  whose  wheel  (3).  with  its  eccentric,  drives  the 
agitator.  The  thermometer  (A)  gives  the  temperature  of  the  water; 
because  of  the  thorough  mixing  of  the  water  by  the  agitator  it  gives 
an  accurate  record  of  the  temperature  of  the  water  throughout  the 
apparatus.  The  thermometer  is  pushed  down  farther  than  is  repre- 
sented in  the  illustration.  It  usually  lies  aside  of  the  tube  (H ) .  The 
air-tube  (B)  also  has  a  thermometer  to  denote  the  temperature  of 
the  air  as  it  is  heated  by  the  man.  The  thermometer  at  B  is  grad- 
uated into  tenths,  while  that  at  A  is  graduated  into  fiftieths.  The 
markings  are  so  far  apart  that  one  one-hundredth  of  a  degree  Fah- 
renheit can  be  read. 

The  temperature  of  the  mouth  is  taken  by  a  thermometer  grad- 
uated into  tenths.  The  rectal  temperature  is  preferable  because  of 
accuracy.  The  bucket  (I)  receives  the  water  from  the  motor  (X), 
and  so  conveys  it  to  the  water-wheel  (H)  that  runs  the  meter  as  an 
aspirator.  The  meter  is  filled  with  water,  and  belongs  to  Voit's  little 
respiration  apparatus.  The  quantity  of  air  that  is  aspirated  within  an 
hour  is  from  5000  to  6000  liters,  which  is  ample  for  respiratory  pur- 
poses. The  instrument  is  made  air-tight  by  means  of  the  door  (K), 
which  is  lined  at  its  outer  edge  with  rubber.  The  whole  apparatus  is 
inclosed  in  over  six  inches  of  sawdust,  the  door  ( K)  having  against 
it  a  sawdust  mattress. 

The  door  is  bound  by  eight  powerful  screw-clamps.  The  air 
enters  the  tube  (H ),  then  passes  through  a  leaden  tube  that  is  coiled 
upon  itself  before  it  reaches  the  person  lying  upon  the  mattress. 

I  have  tested  the  calorimeter  before  and  after  the  performance 
of  my  experiments. 

The  interior  of  the  instrument  is  lighted  up  by  an  Edison 
incandescent  light  of  one-candle  power.  The  patient  is  thus  enabled 
to  spend  his  time  in  reading  a  book  while  the  experimenter  is  making 
his  observations. 

By  placing  a  pulley  outside  the  calorimeter  and  attaching  to  a 
leather  rope  a  fourteen-pound  weight,  the  man  within  the  instrument 
is  able  to  exercise.  The  leather  band  enters  one  of  the  air-holes  of 
the  instrument.  Of  the  entire  amount  of  heat  dissipated,  about 
14  per  cent,  is  thrown  off  by  the  lungs. 

My  little  calorimeter  is  constructed  upon  the  same  plan  as  the 


ANIMAL  HEAT.  347 

instrument  for  men.  In  this — the  animal  calorimeter — the  agitator 
sits  astride  the  inner  cylinder,  outside  of  the  leaden  coils,  and  is  run 
at  the  rate  of  sixty  to  seventy  movements  per  minute  by  means  of  a 
water-motor.  In  other  instruments  the  water  is  occasionally  agitated 
by  means  of  a  hand-contrivance.  Instead  of  the  air  entering  the 
inner  chamber  by  a  straight  tube,  it  traverses  a  tube  coiled  upon 
itself  in  the  water-  reservoir  of  the  instrument  to  enter  the  inclosure 
at  its  base.  The  air  emerges  through  the  opening  at  the  top  to  be 
carried  out  through  the  serpentine  coil  and  thence  through  the 
aspirating  meter.  The  latter  records  at  the  same  time  the  amount 
of  air.  The  constant  activity  of  the  agitator  causes  the  heat  to  be 
equally  diffused  through  the  water  and  so  permits  none  to  be  given 
to  the  air.  The  door  swings  upon  a  hinge.  In  its  center  is  a  glass 
through  which  one  can  readily  see  the  state  of  the  animal  or  the 
apparatus  connected  with  it.  At  its  edge  it  is  lined  with  rubber  anil 
closed  by  powerful  iron  screw  clamps.  In  front  of  the  door  is  a  mat- 
tress of  sawdust  several  inches  thick.  Over  and  around  the  calorime- 
ter, instead  of  the  usual  sawdust  or  felt,  I  used  the  packing  material 
of  wood-fiber  known  as  excelsior.  The  whole  instrument  is  inclosed 
within  a  box  which  has  a  door. 

The  calorimeter  is  sixteen  inches  in  length  and  twelve  inches 
in  diameter.  The  instrument  has  a  circular  opening  through  which 
a  thermometer  graduated  to  one-fiftieth  of  a  degree  Fahrenheit  passes 
into  the  water.  An  opening  is  also  provided  in  the  air-tube  into 
which  a  thermometer  can  be  inserted. 

This  instrument  is  fairly  exact.  By  calculation  it  is  found  that 
the  error  is  5.4  per  cent.  After  tne  performance  of  numerous  experi- 
ments it  was  found  that  the  variations  from  this  number  were  within 
1  per  cent.  Hence  it  may  be  assumed  that  this  is  an  instrument  of 
precision.  For  absolute  accuracy  the  moisture  of  the  air  and  the 
barometric  correction  should  be  made,  but  they  would  not  alter  the 
result  very  perceptibly.  The  instrument  is  always  used  with  the  air 
a  degree  or  so  above  the  temperature  of  the  calorimeter.  The  agi- 
tator is  set  in  motion  for  a  half-hour  before  the  observation  is  com- 
menced. The  room  temperature  for  twenty-four  hours  previously  is 
kept  the  same.  With  these  precautions  the  instrument  works  ac- 
curately. 

By  the  calorimeter  we  are  enabled  to  measure  the  transforma- 
tion of  the  potential  energy  of  the  food  into  heat  and.  at  the  same 
time,  measure  the  number  of  heat  units  produced.  The  total  amount 
of  energy  present  in  the  human  body  might  be  measured  by  com- 


;348  PHYSIOLOGY. 

pletety  burning  an  entire  human  body  in  a  calorimeter.  By  this 
means  it  may  be  determined  how  many  heat  units  are  produced  when 
it  is  reduced  to  ashes.  «, 

If  a  man  were  not  supplied  with  food  he  would  lose  fifty  grams 
of  his  body-weight  every  hour.  This  is  due  to  the  constant  oxidation 
which  occurs,  whereby  the  materials  of  the  body  unite  with  .the  in- 
spired and  circulating  oxygen  to  produce  combustion  and  heat. 

It  is  known  that  any  given  oxidation  will  always  produce  the 
same  amount  of  heat.  Thus,  if  a  gram  of  fat  be  burned  in  a  calorim- 
eter there  will  be  produced  a  certain  and  almost  unvarying  number 
of  heat  units.  By  numerous  experiments  upon  foodstuffs  it  has  been 
determined  by  the  calorimeter  just  the  number  of  heat  units  a  gram 
of  each  will  yield.  Just  as  in  the  calorimeter,  only  far  more  slowly, 
are  the  foodstuffs  within  our  bodies  burned  up.  That  is,  the  presence 
of  oxygen  transforms  the  potential  energy  within  them  into  kinetic. 
Should  the  voluntary  activities  be  at  rest,  the  major  portion  of  this 
energy  is  transformed  into  heat.  The  same  number  of  heat  units 
would  be  produced  within  the  body  as  within  the  calorimeter,  pro- 
vided the  foodstuffs  were  completely  oxidized.  However,  we  know 
that  every  gram  of  proteid  yields  one-third  of  a  gram  of  urea  during 
combustion  within  the  body.  The  urea  has  a  heat  value  of  its  own, 
so  that  the  real  number  of  heat  units  obtained  by  body-combustion 
is  considerably  less  than  that  of  calorimeter  combustion  of  proteids. 
The  units  obtained  from  body  or  tissue  combustion  represent  a 
"physiological  heat  value";  those  gained  from  the  calorimeter,  a 
"physical  heat  value." 

Thermotaxic  Centers. — These  centers  compose  the  thermogenic, 
thermo-inhibitory,  and  thermolytic  centers,  as  the  aim  of  all  is  to 
regulate  the  temperature. 

THERMOGENIC  CENTERS.  —  Spinal  Cord.  —  Destruction  of  the 
spinal  cord  from  the  fifth  dorsal  vertebra  down  permits  the  animal 
to  generate  as  much  heat  as  before  the  operation.  A  drug,  beta- 
tetrahydronaphthylamin,  when  injected  by  the  vein  causes  a  great  in- 
crease of  temperature,,  but  after  a  section  behind  the  tuber  cinereum 
it  fails  to  cause  any  rise  of  temperature.  These  facts  lead  to  the 
conclusion  that  there  are  no  special  thermogenic  centers  in  the  spinal 
cord,  but  that  the  basal  thermogenic  centers  act  through  the  trophic 
centers  in  the  anterior  cornua. 

Brain. — When  a  normal  animal  is  subjected  to  heat  or  cold  it 
regulates  its  temperature  and  keeps  it  at  a  fixed  point.  If,  however, 
the  spinal  cord  is  separated  from  the  brain,  the  spinal  cord  is  not 


ANIMAL  HEAT.  349 

able  to  regulate  the  temperature  at  a  given  degree,  but  its  tempera- 
ture changes  with  the  temperature  of  the  surrounding  air.  These 
facts  also  show  the  importance  of  the  thermotaxic  centers  in  the 
brain  in  the  regulation  of  temperature. 

As  to  the  medulla  oblongata  and  pons,  numerous  punctures  by 
a  probe  two  millimeters  in  width  and  one  millimeter  in  thickness 
caused  a  very  slight  rise  of  temperature,,  which  was  of  a  very  fugitive 
nature.  Cross-section  of  the  pons  is  an  operation  which  cuts  off  the 
afferent  and  efferent  fibers  from  the  thermotaxic  centers  anterior  to 
it  and  permits  heat-production  to  increase  without  any  regulation. 
If  there  are  any  thermogenic  centers  in  the  pons,  puncture  ought  to 
bring  out  the  fact,  as  it  has  done  for  the  thermogenic  centers  located 
in  the  basal  ganglia. 

Any  transverse  section  behind  the  crura  cerebri  or  pons  simply 
cuts  out  the  thermogenic  and  thermo-inhibitory  centers  in  front  of 
the  section  and  permits  the  thermic  apparatus  behind  the  section  to 
elevate  the  temperature.  That  a  greater  rise  of  temperature  should 
ensue  after  pontal  than  after  crural  section  is  quite  in  accord  with 
the  well-known  fact  that  successive  sections  from  before  backward 
cause  a  greater  activity  of  the  spinal-cord  centers  behind  the  section, 
and  also  of  the  trophic  centers. 

Now,  I  have  shown  that  after  the  intravenous  injection  of  beta- 
tetrahydronaphthylamin  in  the  normal  animal  a  great  rise  of  tem- 
perature ensues.  But  after  section  through  the  crura  cerebri  this 
drug  is  powerless  to  raise  the  temperature.  A  needle-point  thrust 
into  the  pons  or  crura  causes  a  fugitive  rise,  and  a  feeble  one.  But  if 
the  needle  goes  into  the  corpora  striata  or  tuber  cinereum  there  is  a 
quite  permanent  and  considerable  elevation  of  temperature.  To  as- 
sume that  a  different  kind  of  thermogenic  center  exists  in  the  pons  is 
begging  the  question. 

In  April,  1884,  I  was  the  first  to  make  a  transverse  section  of 
the  corpora  striata  in  the  cat,  which  was  followed  by  the  temperature 
rising  to  110  Y2°  F.  Afterward  Drs.  Sachs  and  Aronsohn  more 
exactly  localized  the  center  in  the  caudate  nucleus.  I  also  located 
another  thermogenic  center  in  the  optic  thalami,  a  bilateral  puncture 
of  their  anterior  ends  causing  a  rapid  rise  of  temperature  to  109°  F. 
Von  Tangl,  of  Budapest,  has  confirmed  this  fact  by  experiment  upon 
the  brain  of  a  horse.  Upon  more  exact  localization  this  thalamic 
thermogenic  center  was  found  to  be  located  in  the  tuber  cinereum. 
Hence  the  conclusion  that  the  thermogenic  centers  are  located  in  the 
corpus  striatum  and  tuber  cinereum. 


PHYSIOLOGY. 


The  tuber  cinereum  is  also  connected  with  the  vasomotor  appa- 
ratus. In  experiments  to  find  vasotonic  centers  in  the  thalami  I  have 
located  them  in  their  anterior  part.  Later  experiments  have  led 
to  more  exact  data.  After  puncture  of  the  tuber  with  a  fine  probe 
a  gradual  fall  of  arterial  tension  ensued.  In  about  forty  minutes  it 
amounted  to  one-fourth  the  absolute  pressure.  This  fall  invariably 
ensued  in  six  experiments;  so  that  there  seemed  little  doubt  that 
vasotonic  centers  exist  in  the  thalami. 

THERMO-INHIBITORY  CENTERS. — Eulenberg  and  Landois  discov- 
ered about  the  cruciate  sulcus  a  center  whose  ablation  was  followed 


R.T. 

,0^o 

108° 
107° 
106° 


103° 


x 

X"" 

\ 

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\ 

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\ 

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- 

7 

\ 

7 

\ 

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\ 

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\ 

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ao 

6 

5 

IOC 

> 

M 

i8c 

i 

sac 

a6 

3 

Mil 

30 
lutes 

3 

,  firs 

340 
t  day. 

Fig.  78. — Bilateral  Puncture  of  the  Tuber  Cinereum  of  Rabbit  Through 

Roof  of  Mouth. 

by  an  increase  of  temperature.  Prof.  H.  C.  Wood  has  shown  that 
the  increase  is  due  to  augmented  production  of  heat.  I  have  also 
shown  in  the  ca,t  that  at  the  juncture  of  the  suprasylvian  and  post- 
sylvian  fissures  is  another  center  whose  removal  is  followed  by  an 
increase  of  temperature.  This  has  been  confirmed  by  White. 

The  increased  heat-production  after  injury  to  the  Sylvian  and 
cruciate  centers,  the  fall  to  normal,  and  the  subsequent  rise  in  some 
cases  indicate  that  there  is  a  conflict  between  these  centers  and  those 


ANIMAL  HEAT. 


351 


that  lie  beneath  in  an  effort  to  gain  the  mastery.  This  state  of 
things  is  seen  in  the  temperature  of  patients  afflicted  with  fever. 

Puncture,  like  fever  poison,  excites  the  thermogenic  centers. 
Antipyretics  act  as  sedatives  to  them  and  so  reduce  their  excitability. 

Albumoses,  peptones,  and  neurin  have  been  shown  by  Ott  to  pro- 
duce fever. 

Dr.  W.  Hale  White  reports  a  case  in  which  a  bullet  from  a  pistol 
caused  an  injury  of  the  anterior  extremity  of  the  middle  lobe  of  the 


Fig.  79.— Cortex  of  Cat's  Brain. 

g,  Cruciate  thermo-inhibitory  center  of  Eulenberg  and  Landois.    8,  Sylvian 
thermo-inhibitory  center  of  Ott. 

right  hemisphere  and  also  the  third  frontal  convolution,  which  was 
followed  by  a  temperature  of  104.4°  F.  in  less  than  twelve  hours  after 
the  accident. 

Dr.  Page  also  reported  a  case  of  depressed  fracture  of  the  skull 
which  was  about  the  posterior  part  of  the  temporo-sphenoidal  lobe 
and  which  was  followed  by  a  temperature  of  105°  F.  This  tempera- 
ture fell  after  trephining,  and  it  did  not  rise  again.  Fig.  80  shows 


352 


PHYSIOLOGY. 


the  position  of  these  lesions  in  man,  and  they  correspond  roughly 
to  the  position  of  the  cruciate  and  Sylvian  centers  in  the  cat. 

THERMOLYTIC  CENTERS. — These  centers  include  the  cooling  appa- 
ratus of  the  body:  the  polypnceic,  the  sudorific,  and  the  vasomotor 
centers. 

Polypnoea. — Professor  Eichet  found  that  with  the  elevation  of  the 
body-heat  of  an  animal  its  respirations  suddenly  increased  to  350  or 
400  per  minute.  This  form  of  respiration  he  termed  polypnoea.  It 
was  found  that  the  animal  did  not  do  this  from  want  of  oxygen.  An 
animal  pants  to  cool  himself,  while  a  man  perspires  for  the  same 
purpose.  The  role  of  polypncea  is  exclusively  to  regulate  the  tem- 
perature of  the  body. 


Fig.  80. — Lesions  of  Cortex  in  Man  Causing  Elevations  of  Temperature. 

I  have  made  numerous  experiments  to  determine  the  exact  seat 
of  the  polypnoeic  center.  To  establish  a  center  three  things  are 
necessary:  (1)  that  its  abolition  causes  the  phenomena  to  disappear, 
(2)  that  irritation— mechanical,  chemical,  or  electrical — causes  the 
phenomena  to  be  present,  and  (3)  that  the  part  of  the  nervous  system 
exhibiting  these  peculiarities  be  circumscribed  in  extent.  After  nu- 
merous observations  and  experiments  it  was  found  that  pressure 
upon  the  tuber  cinereum  with  a  pledget  of  cotton,  or  even  slight 
puncture,  increased  the  normal  respirations  to  the  point  of  polypnoea. 
Complete  puncture  in  a  normal  animal  was  followed  by  a  rise  to 
106°  F.  within  two  hours,  even  though  the  animal  were  bound  down 
and  had  been  subjected  to  considerable  shock. 

If  now  the  animal  be  heated  in  whom  the  tuber  is  punctured,  there 


ANIMAL  HEAT.  353 

will  result  no  polypncea,  even  though  a  temperature  of  107°  F.  be 
reached.  I  am  convinced  that  the  tuber  cinereum  is  a  center  of  polyp- 
ncea  and  thermotaxis.  When  heat  is  thrown  on  the  body  the  polypnceic 
center  telegraphs  the  respiratory  center  to  work  more  rapidly  to 
throw  off  more  moisture  by  the  expired  air. 

The  afferent  nerves  of  the  thermotaxic  apparatus  are  probably 
those  nerves  in  the  skin  administering  to  the  "  hot iy  and  "  cold " 
spots. 

Regulation  of  Loss  of  Heat,  or  Thermolysis. — Heat  is  lost  by  an 
animal  in  various  ways.  It  may  be  by  direct  radiation  and  conduction 
from  the  skin,  by  the  extraction  of  heat  during  the  process  of  evapo- 


Fig.  81. — Curves  of  Temperature  and  Respiration  when  Cortex  is 
Removed  and  the  Animal  is  Artificially  Heated. 

rating  perspiration,  by  warming  the  respired  air,  and  by  the  discharge 
of  urine  and  faeces. 

SKIN  BADIATION  AND  CONDUCTION. — The  skin  is  the  main  means 
of  escape  of  the  bodily  heat.  Nearly  three-fourths  of  the  heat  which 
escapes  from  the  economy  does  so  through  the  skin  as  a  means. 

A  marked  difference  between  the  temperature  of  the  skin  and 
that  of  the  surrounding  atmosphere  constitutes  a  prime  factor  in 
radiation.  When  the  enveloping  medium  is  very  cold  radiation  from 
the  skin's  surface  is  very  rapid. 

The  cutaneous  circulation  has  considerable  to  do  with  the  dissi- 
pation of  heat.  The  caliber  of  the  peripheral  vessels  is  governed  by 
the  vasomotor  system,  which  is  itself  under  the  guidance  of  the 
central  nervous  svstem. 


354 


PHYSIOLOGY. 


External  heat  reflexly  causes  dilatation  of  the  cutaneous  vessels, 
so  that  at  such  times  the  skin  becomes  red  and  engorged.  It  contains 
more  fluids  and  thus  is  a  better  conductor  of  heat.  More  blood  being 
at  the  body  surface  allows  of  greater  and  more  rapid  loss  through 
radiation. 

External  cold  reflexly  causes  a  contracting  of  the  peripheral  ves- 
sels; so  that  their  lumina  are  narrowed.  In  consequence  there  is  less 
blood  circulating  in  the  skin,  which  appears  pale  and  contains  less 
fluid;  so  that  the  radiation  of  heat  is  markedly  hindered. 

By  reason  of  nervous  stimulation  the  sweat-glands  are  at  times 
made  to  functionate  very  freely;  whereupon  the  skin's  surface  be- 


in 

lof 


40.  702 


Fig.  82. — Curve  of  Temperature  and  Respiration  when  the  Tuber  Cinereum 
is  Destroyed  and  the  Animal  is  Artificially  Heated. 

comes  bathed  in  a  sensible  perspiration.  For  the  conversion  of  this 
moisture  into  vapor  heat  is  necessary.  It  is  by  the  abstraction  of  this 
heat  from  the  underlying  tissues  that  the  body  owes  much  of  its  loss 
when  its  parts  are  hyperpyrexial. 

The  covering  of  the  body  by  clothing  during  the  various  seasons 
of  the  year  contributes  a  great  deal  to  .the  proper  regulation  of 
loss  of  heat,  so  that  the  mean  temperature  may  be  maintained  fairly 
constant. 

FEVER. — The  process  of  fever  is  one  of  absorbing  interest  during 
every  period  of  a  physician's  life.  The  constant  level  of  temperature 
in  man  is  accounted  for  by  two  theories:  One  that  it  is  due  to 
changes  in  heat  production;  the  other,  held  by  a  minority,  that  it  is 


DAY  AFTER. 
CHILL 


PER.IODS.  i 


m  w  ggffl 


Fig.  83. — Heat  Production  and  Heat  Dissipation  in  Man  during  a  Paroxysm 
of  Malaria]  Fever — a  Great  Increase  of  Heat  Production. 


356  PHYSIOLOGY. 

kept  so  by  changes  in  heat  dissipation  under  the  varying  conditions 
of  external  temperature. 

In  a  case  of  fever  generated  by  the  malarial  parasite  I  found 
with  the  human  calorimeter  an  increased  production  of  heat  as  the 
primary  cause  of  the  fever.  In  the  case  of  fever  generated  by  the 
subcutaneous  injection  of  putrid  blood  I  found  a  fever  caused  by 
an  increased  production  of  heat  in  the  animal. 

As  a  rule,  it  is  true  that  fever  is  set  up  by  an  increase  of  heat 
production  beyond  that  of  heat  dissipation.  But  when  this  is  once 
established  the  fever  continues,  not  from  an  excessive  production, 
but  from  an  altered  relation  between  heat  production  and  heat 
dissipation. 

That  the  basal  thermogenic  centers,  the  corpus  striatum  and 
tuber  cinereum,  play  a  prominent  part  in  the  production  of  fever  is 
proved  by  the  fact  that  putrid  blood  and  betatetrahydronaphthylamin 
both  produce  a  rise  of  temperature.  After  a  section  behind  the  tuber 
cinereum  they  are  powerless  to  elevate  the  temperature. 

Antipyrin  reduces  the  temperature  by  an  action  upon  the  cor- 
pora striata. 

Experiments  in  my  laboratory  by  Dr.  W.  S.  Carter  proved  that 
while  the  temperature  of  the  body  has  a  rhythm,  there  was  no  rhythm 
in  either  heat  production  or  heat  dissipation. 

All  recent  researches  go  to  show  that  fever  is  not  a  fire  that  is 
continuously  kept  up  by  an  excessive  oxidation  of  the  constituents  of 
the  human  body.  For  instance,  if  the  amount  of  water  flowing  into 
a  vessel  partly  filled  with  water  is  equal  to  2,  and  the  amount  ffoing 
out  is  equal  to  2,  the  level  of  the  water  will  be  the  same.  But  if  the 
amount  of  water  going  into  the  vessel  is  equal  to  3  and  the  amount 
going  out  equal  to  2,  the  level  of  the  water  will  rise.  If,  however, 
the  amount  going  into  the  vessel  should  suddenly  fall  to  1  and  the 
amount  going  out  should  do  the  same,  the  level  of  the  water  would 
be  nearly  the  same  as  before.  If,  now,  you  substitute  for  the  amount 
of  water  going  in  the  amount  of  heat  produced,  and  for  the  water 
going  out  the  amount  of  heat  dissipated,  and  the  level  of  the  water 
as  the  height  of  temperature,  it  is  easy  to  see  how  a  diminished  pro- 
duction and  dissipation  of  heat  due  to  want  of  food  and  the  waste  of 
the  body  by  the  fever  process,  may  still  keep  up  a  high  fever,  al- 
though both  are  diminished  below  what  is  generated  and  dissipated 
in  a  state  of  health. 

Postmortem  Temperature. — Usually  after  death  the  body  cools 
gradually,  depending  upon  the  temperature  of  the  external  atmos- 


ANIMAL  HEAT.  357 

phere  and  the  body-surface.  The  body  of  a  child  or  emaciated  sub- 
ject cools  more  rapidly  than  does  that  of  a  well-developed  and  well- 
nourished  adult  body. 

A  temporary  increase  of  postmortem  temperature  is  due  to  the 
change  of  myosinogen  into  myosin  and  to  those  series  of  chemical 
changes  immediately  succeeding  death. 

When  death  has  occurred  from  tetanus,  acute  rheumatism,  ty- 
phoid, small-pox,  cholera,  or  injuries  to  the  brain,  there  is  noted  a 
marked  postmortem  rise  in  temperature. 


CHAPTER  XI. 

THE  MUSCLES. 

COVERING  up  the  bones  and  attached  to  their  surfaces  at  certain 
definite  places  is  the  soft,  red,  fleshy  portion  of  the  body :  the  muscular 
substance.  This  consists  of  not  one  homogeneous  environing  mass,  but 
a  great  number  of  distinct  fleshy  masses,  called  muscles.  These  are 
of  various  forms  and  sizes;  number  about  four  hundred;  and  are, 
for  the  most  part,  arranged  in  pairs.  It  is  mainly  to  the  shape  and 
disposition  of  these  muscles  that  the  body  owes  the  regularity  of  its 
contour. 

It  is  by  the  power  of  these  skeletal  muscles  that  the  animal  is 
able  to  move  about,  procure  means  of  sustenance,  care  for  its  young, 
etc. ;  but  it  must  be  borne  in  mind  that  muscles — not  so  powerful  as 
are  the  skeletal  muscles,  but  muscles,  nevertheless — are  contained 
within  the  viscera  and  blood-vessel  walls.  These  muscles  have  very 
important  functions  to  perform  in  aiding  the  processes  of  metab- 
olism: that  balance  which  when  disturbed  produces,  not  health,  but 
disease. 

Any  animal  motion  means  muscle.  Muscular  tissue  is  empowered 
with  contractility;  that  is,  an  ability  to  shorten  itself  when  acted  upon 
by  any  stimulus.  By  its  shortening  it  produces  movement  to  parts  to 
which  one  or  both  of  its  ends  are  attached.  The  resultant  motions 
may  be  the  very  common  ones  of  walking,  running,  various  manual 
employments,  etc.,  or  the  peristaltic  movements  of  stomach  and  in- 
testines, or  the  variations  in  the  sizes  of  the  lumen  of  the  blood- 
vessels. Any  animal  movement  should  at  once  recall  to  the  mind  of 
the  student  that  it  is  the  resultant  of  some  muscular  contractility 
produced  by.  the  influence  of  a  stimulus  to  it,  whether  that  be  nerv- 
ous, electrical,  mechanical,  or  thermal. 

Muscular  tissue  consists  of  fibers  bound  together  into  those  dis- 
tinct organs  already  mentioned  as  muscles,  and  in  this  condition  is 
known  as  the  meat  of  animals. 

In  the  fine  anatomy  of  the  muscles  I  have  followed  the  writings 
of  Professor  Shaefer,  as  appears  in  Quain's  "Anatomy,1"  of  which 
this  is  an  abstract. 
(358) 


THE  MUSCLES.  359 

Varieties.  —  When  seen -under  the  microscope,  these  fibers  are 
found  to  be  cross-striped,  or  striated;  as  many  of  them  are  under  the 
control  of  the  will,  they  are  usually  spoken  of  as  being  voluntary. 

In  the  coats  of  the  blood-vessels  and  the  hollow  viscera  is 
another  variety  of  muscular  fibers  often  making  a  distinct  layer  or 
layers  to  these  organs.  In  this  kind  the  fibers  do  not  have  the  cross- 
striped  appearance,  but  are  plain,  or  unstriped.  Nearly  all  of  these 
are  not  under  the  control  of  the  will,  and  are,  hence,  involuntary.  It 
must  here  be  noted,  however,  that  the  muscle  of  the  heart — which, 
as  everyone  knows,  is  an  involuntary  muscle — is  exceptional  to  this 
class  of  muscle  in  that  its  fibers  are  very  plainly  cross-striped.  Never- 
theless, it  presents  differences  from  the  striped  fibers  of  skeletal 
muscles;  so  that  it  has  become  customary  with  very  many  authors 
to  class  it  under  the  separate  title  cardiac  muscular  tissue. 

The  muscular  fibers  of  the  skeleton  are  generally  collected  into 
distinct  organs  of  various  sizes  and  shapes  which  have  at  each  end 
a  tendon  by  which  they  are  attached  to  the  skeleton. 

The  fibers  of  the  muscles  are  collected  together  into  bundles, 
called  fasciculi.  In  the  fasciculi  the  fibers  are  parallel,  so  that  the 
fasciculi  wind  from  one  tendinous  end  to  the  other,  except  in  a  few 
muscles  like  the  rectus  abdominis.  In  this  instance  the  body  of 
the  muscle  is  interrupted  by  interposed  tendinous  tissue.  The  fas- 
ciculi themselves  do  not  mingle  with  one  another  and,  for  the  most 
part,  run  parallel,  although  in  many  cases  they  converge  to  their 
tendinous  endings. 

The  covering  of  the  entire  muscle  is  termed  the  epimysium,  and 
is  a  connective-tissue  envelope.  The  covering  of  areolar  tissue  which 
insheathes  the  fasciculi  of  the  muscle  is  spoken  of  as  the  perimysium. 
The  latter,  a  septum  from  the  epimysium,  furnishes  to  each  fascicu- 
lus a  special  covering  as  well  as  furnishing  it  with  blood-vessels  and 
nerves. 

Within  each  compartment  lie  a  number  of  muscle-fibers  which 
are  usually  parallel  to  one  another  and  held  together  by  a  very 
delicate  reticular  connective  tissue.  This  areolar  network  is  called 
the  endomysium,  but  does  not  make  a  continuous  covering  and  so 
cannot  be  said  to  form  sheaths  for  them.  Each  fiber  of  the  muscle, 
however,  has  a  tubular  sheath,  but  this  sheath  is  not  composed  of  the 
areolar  tissue  just  mentioned.  The  special  function  of  the  areolar 
tissue  seems  to  be  to  connect  the  fasciculi  and  fibers,  and  to  support 
and  conduct  the  blood-vessels  and  nerves  in  their  ramifications  be- 
tween the  various  parts. 


360  PHYSIOLOGY. 

FASCICULI  in  form  are  prismatic,  so  that  a  transverse  section 
shows  an  angular  outline.  The  thickness  of  a  fasciculus,  as  well  as 
the  number  of  fibers  of  which  it  is  composed,  varies.  The  texture  of 
a  muscle,  whether  coarse  or  fine,  depends  upon  the  large  or  small 
fasciculi  contained  within  it;  thus,  the  glutei  are  coarse,  the  muscles 
of  the  eye  fine. 

The  length  of  the  fasciculi  is  not  always  the  same  as  the  length 
of  the  muscle;  this  characteristic  depends  upon  the  arrangement  of 
the  tendons  to  which  the  muscle  is  attached.  When  the  tendons  are 
attached  to  the  ends  of  a  long  muscle,  as  the  sartorius,  the  fasciculi 
run  from  one  end  of  the  muscle  to  the  other  and  so  are  of  consid- 
erable length.  However,  a  long  muscle  may  be  made  up  of  a  series 
of  short  fasciculi  attached  obliquely  to  one  another  by  beveled  ends. 
Short  fasciculi  thus  attached,  as  in  the  rectus  muscle  of  the  thigh, 
have  stronger  action  than  where  they  run  the  extent  of  the  muscle. 

FIBERS. — The  form  of  the  muscle-fibers  is  cylindrical  or  prismatic 
with  rounded  angles.  Their  diameter  varies  very  considerably,  even 
in  each  muscle,  although  a  certain  standard  is  found  to  exist  in  every 
muscle.  The  largest  human  fibers  average  one-tenth  of  an  inch  in 
diameter,  and  from  that  size  to  one  two-hundred-and-fiftieth  of  an 
inch  fibers  may  be  found.  Between  the  size  of  the  muscle  and  that  of 
its  fibers  there  is  no  constant  relation. 

The  length  of  the  muscular  fibers  does  not  generally  exceed  one 
and  one-half  inches.  Thus,  in  a  long  fasciculus,  the  fibers  do  not 
reach  its  whole  length,  but  end  in  a  rounded  or  tapering  end  invested 
with  sarcolemma  and  cohering  with  neighboring  fibers.  There  is,  as 
a  rule,  no  anastomosis  or  division  of  the  fibers  of  a  muscle,  except  in 
the  tongue  of  a  frog,  where  they  branch  beneath  the  mucous  mem- 
brane to  which  they  are  attached.  The  same  thing  has  been  observed 
in  the  tongue  of  man. 

SARCOLEMMA. — The  sarcolemma  is  a  tubular  sheath  inclosing  the 
soft  substance  of  the  muscle.  It  is  an  elastic,  transparent,  homoge- 
neous membrane;  it  is  rather  tough  and  can  remain  intact  even 
though  the  muscle  be  ruptured.  Upon  its  inner  side  are  found  nuclei 
which,  howrever,  belong  to  the  muscle  rather  than  to  the  inclosing 
membrane. 

Structure. — With  a  low  magnifying  power,  the  muscle  presents 
clear  pellucid  fibers  which  are  cross-striped  with  bands  alternately 
dark  and  light.  That  this  striation  is  not  on  the  surface  alone,  but 
extends  throughout  the  substance  of  the  muscle,  is  readily  demon- 
strated by  altering  the  focus  of  the  microscope.  The  stripes  do  not 


THE  MUSCLES. 


3(31 


12 


Fig.  84. — Histology  of  Muscular  Tissue.     (ELLENBERGER.) 

1.  Diagram    of    part    of    a    striped    muscular    fiber.     8,    Sarcolemma.      Q, 
Transverse  stripes.    F,  Fibrillae.     K,  Muscle  nuclei.    N,  Nerve-fibers  entering 
it  with  A,  its  axis  cylinder,  and  Kiihnes  motorial  end-plate,  E,  seen  in  profile. 

2.  Transverse   section   of   part   of   a   muscular   fiber,   showing   Cohnheim's 
areas,  C. 

3.  Isolated  muscular  fibrillae. 

4.  Part  of  an  insect's  muscle,  greatly  magnified.     A,  Krause-Amici's  line 
limiting  the  muscular  cases.     B,   The  doubly  refractive  substance.     C,   Hen- 
sen's  disc.    D,  Singly  refractive  substance. 

5.  Fibers  cleaving  transversely  into  discs. 

6.  Muscular  fiber  from  the  heart  of  a  frog. 

7.  Development  of   a   striped   muscle   from   a   human   foetus   at   the   third 
month. 

8.  9.  Muscular  fibers  of  the  heart.     C,   Capillaries.     B,   Connective  tissue 
corpuscles. 

10.  Smooth  muscular  fibers. 

11.  Transverse  section  of  smooth  muscular  fibers. 

12.  Muscular  fibers  with  tendon. 

13.  Interfibrillary  muscular  nerves. 


362  PHYSIOLOGY. 

occur  on  the  sarcolemma,  but  throughout  the  sarcous  substance  in- 
closed by  the  former. 

The  breadth  of  the  bands  is  about  Vi-ooo  inch,  so  that  eight  or 
nine  dark  bands  may  be  counted  in  1/1000  inch.  While  this  is  the 
common  breadth  in  human  muscle,  yet  they  are  much  narrower  in 
different  parts;  so  that  there  may  be  twice  as  many  bands  existing 
in  the  space  just  mentioned.  This  striation  is  found  in  all  muscles 
attached  to  the  skeleton,  in  the  heart,  pharynx,  upper  oesophagus, 
diaphragm,  urethral  sphincter,  external  anal  sphincter,  as  well  as 
in  the  muscles  of  the  middle  ear. 

When  a  muscle  is  deeply  focused,  the  appearance  of  the  striae 
is  somewhat  altered;  a  finely  dotted  line  is  seen  to  pass  across  the 
middle  of  each  light  band.  This  is  supposed  to  represent  Krause's 
membrane  stretching  across  the  fiber  and  attached  to  the  surface  of 
the  sarcolemma.  However,  there  is  reason  to  believe  that  the  ap- 
pearance of  a  dotted  line  in  this  position  in  the  fresh  fiber  is  due  to 
the  peculiar  optical  condition  of  the  tissue. 

A  fine,  clear  line  is  sometimes  seen  in  the  middle  of  each  dark 
band,  and  is  known  as  the  line,  or  disc,  of  Hens  en. 

Since  there  seems  to  be  such  variance  as  to  muscle-structure  and 
so  many  different  names  are  met  with  in  text-books,  it  might  be  well 
to  call  the  student's  attention  to  the  fact  that  Dobie's  line,  Amici's 
line,  and  Krause's  membrane  are  terms  used  to  describe  the  same 
condition.  They  designate  the  dark  line  in  the  white  band.  Hen- 
sen's  line  occurs  in  the  dark  bands. 

In  addition  to  the  cross-striping,  the  fiber  of  the  muscle  has 
longitudinal  striation.  WThen  a  muscle  has  been  very  carefully  teased 
with  fine  needles  after  having  been  previously  hardened  in  spirits, 
an  interesting  result  follows.  The  muscle-fibers  break  up- into  fine, 
longitudinal  elements  of  a  rounded  or  angular  section  and  which  run 
from  end  to  end  of  the  fiber.  These  have  been  very  aptly  termed 
muscle-columns,  or  sarcostyles. 

Each  sarcostyle  appears  to  consist  of  a  row  of  elongated  pris- 
matic particles  with  clear  intervals.  These  particles  are  termed 
sarcous  elements.  The  sarcostyles  in  some  muscles  are  striated  longi- 
tudinally. This  appearance  has  led  some  authors  to  believe  that  they 
are  composed  of  still  finer  elements,  or  fibrils. 

Under  some  conditions,  the  fibers  show  a  tendency  to  cleave 
across  in  a  direction  parallel  to. the  bands,  and  even  to  break  up  into 
transverse  plates,  or  discs.  The  latter  are  made  up  by  the  lateral 
cohesion  of  the  sarcous  elements  of  adjacent  sarcostyles.  To  the  for- 


THE  MUSCLES.  353 

mation  of  such  discs,  therefore,  every  sarcostvle  furnishes  a  particle, 
which  coheres  with  its  neighbors  on  each  side,  and  this  with  perfect 
regularity. 

Sarcoplasm  is  the  intercolumnar  substance  by  which  the  sarco- 
st}rles  are  united  into  the  muscle-fibers.  It  is  the  protoplasm  of  the 
muscle-corpuscles,  and  forms  a  fine  network  throughout  the  whole 
muscular  fiber. 

From  an  examination  of  the  aforementioned  facts,  Bowman  was 
induced  to  believe  that  the  division  of  the  fiber  into  fibrils,  or  sarco- 
styles,  was  merely  a  phenomenon  of  the  same  kind  as  the  separation 
into  discs,  only  a  more  common  occurrence. 

COHNHEIM'S  AREAS. — If  a  transverse  section  be  made  of  a  mus- 
cular fiber,  or  the  surface  of  a  separated  disc  be  examined  with  a 
strong  objective,  there  appear  in  the  field  small  polygonal  areas 
separated  by  fine  lines.  In  acid  preparations  they  give  the  appear- 
ance of  a  network.  These  areas  represent  sections  of  the  muscle- 
columns,  and  are  usually  designated  as  Colirilmm's  areas.  The  line 
between  them  represents  the  sarcoplasm,  or  intercolumnar  substance. 

When  a  muscle-fiber  placed  in  fresh  serum  is  examined,  fine, 
longitudinal  lines  are  seen  running  through  the  cross-striping.  If, 
now,  a  weak  acid  is  added  to  swell  the  muscular  substance  and  render 
it  more  transparent,  these  lines  can  be  traced  from  end  to  end  of  the 
fiber.  By  careful  management  of  the  microscope,  it  is  found  that  these 
lines  are  really  the  optical  section  of  the  planes  of  separation  between 
the  sarcostyles;  that  is  to  say,  the  optical  effect  of  the  sarcoplasm,  or 
intercolumnar  substance.  The  sarcoplasm,  in  transverse  section,  pre- 
sents the  aspect  of  network ;  in  longitudinal  optical  section  it  has  the 
appearance  of  fine,  parallel  lines.  The  student  can  readily  imagine 
how  these  effects  can  be  produced  by  the  presence  of  a  small  amount 
of  interstitial  substance  between  closely  packed  prismatic  columns. 

In  most  muscular  fibers  the  sarcoplasm  exhibits  a  peculiarity  of 
arrangement  which  has  a  very  characteristic  influence  upon  the  op- 
tical appearance  of  the  fiber.  In  a  longitudinal  view  of  fresh  muscle, 
the  lines  representing  intercolumnar  sarcoplasm  present  at  regular 
intervals  along  their  course  rather  marked  enlargements.  These  en- 
largements lie  in  the  bright  cross-stria?,  either  in  their  middle  or  near 
their  junction  with  the  dim  cross-stripes.  These  sarcoplasm  nodules 
have  the  appearance  of  dots  upon  fine  longitudinal  lines  which  run 
through  the  muscle;  in  the  more  extended  fibers  these  dots  are  in 
double  rows.  In  less  extended  parts  they  are  thicker  and  blend 
together  in  the  middle  of  the  bright  striae. 


364  PHYSIOLOGY. 

Structure  of  the  Wing-muscles  of  Insects. — The  study  of  these 
muscles  has  furnished  the  key  to  the  comprehension  of  the  intimate 
structure  of  muscle.  As  to  their  structure,  the  wing-fibers  are  in 
complete  agreement  with  ordinary  muscles. 

Wing-fibers  occur  in  large  bundles  of  muscle-columns  or  sarco- 
styles imbedded  in  a  considerable  amount  of  granular  sarcoplasm, 
while  the  whole  of  the  structure  is  inclosed  within  a  sarcolemma. 
The  nuclei  are  scattered  here  and  there.  The  quantity  of  sarco- 
plasm in  wing-muscle  is  relatively  far  greater  than  in  the  ordinary 
muscle. 

When  wing-muscle  has  been  carefully  teased  into  muscle-col- 
umns, or  sarcostyles,  it  is  found  that  they  contract  while  the  sarco- 
plasm is  quiescent.  The  muscle-columns  can  then  be  very  carefully 
studied,  when  they  show,  like  other  muscles,  the  alternate  bright  and 
dark  cross-striping.  Each  bright  stria  is  bisected  by  a  line  which  is 
the  optical  section  of  a  transverse  membrane:  the  membrane  of 
Krause.  These  membranes  divide  the  fibers  into  a  series  of  seg- 
ments, called  sarcomeres. 

In  a  muscle  hardened  by  spirits  each  sar  comer  e  is  seen  to  contain  : 
(1)  in  its  middle,  a  strongly  refracting,  disklike  sarcous  element;  (2) 
at  either  end  (next  the  membrane  of  Krause)  a  clear  interval  occu- 
pied by  hyaline  substance.  With  strong  lenses  the  sarcous  elements 
can  be  made  out  to  be  composed  of  a  sarcous  substance  which  stains 
Avith  logwood;  it  is  pierced  by  short,  tubular  canals  which  extend 
from  the  clear  interval  as  far  as  the  middle  of  the  disc.  It  is  these 
canals  which  give  to  the  sarcous  element  its  longitudinal  striping. 

If /for  any  reason,  the  sarcostyle  becomes  extended,  the  sarcous 
elements  tend  to  separate  into  two  parts  with  an  interval  between 
them ;  vice  versa,  if  the  muscle  be  contracted  or  retracted  the  sarcous 
elements  tend  to  encroach  upon  the  clear  intervals.  At  the  same 
time  the  sarcous  elements  become  swollen,  so  that  the  sarcomeres 
are  bulged  out  at  their  middle  and  contracted  at  their  ends. 

Changes  in  Contraction. — When  these  muscles  contract,  the  sar- 
cous elements  become  bulged  out  and  shortened,  while  the  fluid  of 
the  clear  interval  becomes  relatively  diminished  in  amount.  The 
ends  of  the  sarcomeres  are  thereby  contracted  opposite  the  mem- 
branes of  Krause,  so  that  the  sarcostyles  become  moniliform.  This 
alteration  in  the  shape  of  the  sarcostyle  necessarily  affects  the  sarco- 
plasm which  lies  in  their  interstices.  It  must  become  squeezed  out  of 
the  parts  which  are  opposite  the  bulgings  of  the  sarcostyles  and  into 
those  parts  which  are  opposite  their  constrictions.  In  other  words, 


THE  MUSCLES.  365 

the  sarcoplasm  must  accumulate  in  greater  quantity  opposite  the 
clear  bands  and  the  membranes  of  Krause,  and  must  necessarily 
diminish  in  amount  opposite  the  sarcous  elements. 

In  the  living  muscle  this  change  in  the  position  of  the  sarcoplasm 
during  contraction  can  be  observed;  the  muscle-columns  tend  to 
cause  the  contracted  parts  to  appear  dark,  the  bulged  parts  bright, 
in  comparison. 

Appearance  of  Muscle  under  Polarized  Light. — Briicke  was  the 
first  to  point  out  that  the  fiber  is  not  composed  entirely  of  a  double 
refracting,  or  anisotropous,  substance.  In  addition  there  is  a  cer- 
tain amount  of  singly  refracting,  or  isotropous,  material.  This 
investigator  points  out  that  there  is  a  difference  between  the  ap- 
pearances presented  by  living  muscle  examined  in  its  own  plasma  and 
those  of  dead  and  hardened  muscle  examined  in  glycerin.  In  living 
muscle  nearly  the  entire  fiber  is  doubly  refracting,  the  isotropous 
substance  occurring  only  as  fine  transverse  lines  or  as  rows  of  rhom- 
boidal  dots  which  are  united  to  one  another  across  the  anisotropous 
substance  by  fine  longitudinal  lines.  Sarcous  element  is  anisotropic ; 
sarcoplasm  is  isotropic. 

Nuclei. — In  muscles  that  are  cross-striped  are  found  a  number 
of  clear,  oval  nuclei.  They  are  sometimes  spoken  of  as  muscle-cor- 
puscles. In  mammalian  muscle  they  usually  lie  upon  the  inner  sur- 
face of  the  sarcolemma.  In  the  muscles  of  the  frog  and  reptiles  the 
nuclei  lie  in  the  substance  of  the  fiber  surrounded  by  a  small  amount 
of  protoplasm.  When  the  nuclei  lie  immediately  beneath  the  sarco- 
lemma they  are  more  or  less  flattened.  Each  nucleus  contains  one  or 
two  nuclei.  Mitotic  figures,  denoting  division  of  the  nuclei,  have 
been  observed.  The  nuclei  are  not  very  readily  seen  in  fresh  muscle, 
due  to  their  being  of  the  same  refractive  index  as  the  sarcous  sub- 
stance. Only  after  they  have  undergone  some  spontaneous  change  or 
acetic  acid  has  been  added  to  the  specimen  can  they  be  readily  dis- 
cerned. 

In  the  rabbit  and  rays  of  fishes  some  of  the  voluntary  muscles 
present  differences  from  others,  both  as  to  appearance  and  mode  of 
action.  Thus,  while  most  of  the  voluntary  muscles  are  pale  and  con- 
tract forcibly  when  irritated,  the  soleus  and  semitendinosus  show 
different  characteristics.  They  are  of  deeper  color  and  respond  with 
slow,  prolonged  contractions  when  stimulated.  Thus,  in  these  ani- 
mals there  are  red  and  white  muscles. 

In  other  animals,  this  distinction  of  muscles  is  not  found  as  re- 
gards a  whole  muscle,  but  may  affect  individual  fibers.  Thus,  in  the 


366  PHYSIOLOGY. 

diaphragm  many  of  the  fibers  have  numerous  nuclei  imbedded  within 
the  protoplasm  so  as  to  form  an  almost  continuous  layer  beneath  the 
sarcoleinma. 

Relation  to  Tendons. — When  a  muscle  terminates  in  a  tendon,  it 
is  found  that  the  muscular  fibers  either  run  in  the  same  direction  as 
the  fibers  of  the  tendon  or  join  with  the  tendon  at  an  acute  angle. 
According  to  Toldt,  the  delicate  connective-tissue  elements  covering 
the  several  muscular  fibers  pass  from  the  latter  directly  into  the  con- 
nective-tissue elements  of  the  tendon.  According  to  another  author, 
the  ends  of  the  muscular  fibers  are  believed  to  be  fastened  to  the 
smooth  tendons  by  means  of  a  special  cement.  However,  it  is  probable 
that  the  areolar  tissue  which  lies  between  the  tendon-fibers  passes 
between  the  ends  of  the  muscular  fibers  to  be  gradually  lost  in  the 
interstitial  connective  tissue. 

Blood-vessels  of  Muscle. — The  blood-vessels  to  the  muscles  are 
very  numerous.  The  average  muscle  leads  such  an  active  life  that 
its  nourishment  and  repair  material  must  be  in  proportionate  rela- 
tion. Unlike  the  organs,  as  the  kidney  and  spleen,  which  usually 
are  supplied  by  one  artery  and  vein,  muscles  receive  several  branches 
from  various  arteries  which  pierce  the  muscle  at  different  points 
along  its  course. 

The  artery  and  vein  usually  are  in  close  proximity,  being  held 
in  position  by  the  connective  tissue  upon  the  pefimysium.  The  capil- 
laries lie  between  the  muscle-fibers  in  the  endomysium,  but  outside  of 
the  sarcolemma.  Here  the  capillaries  are  small,  and  form  a  fine  net- 
work with  narrow,  oblong  meshes,  which  are  stretched  out  in  the 
direction  of  the  fibers.  The  capillaries  have  both  longitudinal  and 
transverse  vessels.  The  lymph  that  is  destined  to  support  the  sarcous 
substance  must  pass  through  the  sarcolemma  to  reach  the  same. 

Muscle  Nerve-supply.  —  The  nerve-supply  to  muscles  is  both 
motor  and  sensory.  Each  muscle- fiber  receives  a  motor  nerve-fiber. 
The  trunk  of  the  motor  nerve,  as  a  rule,  enters  the  muscle  at  its 
geometrical  center  (Schwalbe)  ;  thus,  the  point  of  entrance  in  a  long, 
spindle-shaped  muscle  lies  near  its  middle.  At  this  "geometrical 
center"  there  is  the  point  of  least  disturbance  during  contraction  of 
the  muscle.  After  the  trunk  of  the  nerve  pierces  the  muscle  it 
proceeds  to  divide  dichotomously  until  there  are  just  as  many  nerve- 
fibers  as  muscle-fibers.  A  nerve-fiber  now  enters  each  muscle-fiber,  to 
do  which,  of  course,  it  must  pierce  the  sarcolemma.  The  point  of 
entrance  forms  an  eminence  known  as  Doyere's  eminence,  or  material 
end-plate.  At  this  point  the  sheath  of  the  nervo-fibor  becomes  con- 


THE  MUSCLES.  36? 

tinuous  with  the  sarcolemma.  The  eminence  itself  consists  of  a 
mass  of  protoplasm  (sarcoplasm)  containing  grannies  and  nuclei. 
Beneath  the  sarcolemma  the  original  nerve-fiber  is  broken  up  into  a 
number  of  divisions,  spoken  of  as  nerve-endings.  These  are  divisions 
of  the  axis-cylinder  which  are  spread  over  the  sarcous  substance 
without  piercing  it.  To  this  branched  arrangement  of  the  nerve- 
endings  Kiihne  gave  the  name  motor  spray. 

The  nerve-endings  are  thus  confined  to  very  small  areas  on  the 
muscle-fibers  which  have  been  termed  by  the  same  author  fields  of 
innervation.  As  a  rule,  each  muscle-fiber  has  but  one  such  area;  it 
is  the  exception  to  find  more  than  one,  but  as  many  as  eight  have 
been  found  in  very  long  fibers. 

Sensory  fibers  are  also  found  in  muscles,  for  it  is  through  their 
presence  that  we  obtain  muscle  sensibility.  They  seem  to  be  dis- 
tributed upon  the  outer  surface  of  the  sarcolemma,  where  there  is 
formed  a  plexus.  This  plexus  winds  around  the  muscle-fiber. 

Cardiac  Muscle. — Some  mention  has  previously  been  made  con- 
cerning cardiac  muscle,  so  that  at  this  point  only  its  most  striking 
peculiarities  will  be  mentioned,  and  that  cursorily,  (a)  It  is  a 
striped  muscle.  However,  its  striations  are  not  nearly  so  distinctly 
marked  as  are  those  of  voluntary  muscle.  Occasionally  it  is  seen 
to  be  marked  longitudinally,  (b)  Cardiac  muscle-fibers  possess  no 
sarcolemma.  (c)  Its  fibers  branch  and  anastomose,  (d)  The  nucleus 
is  placed  in  the  center  of  each  cell.  One  author  says  that  cardiac 
muscle  stands,  physiologically,  midway  between  striped  and  unstriped 
muscle.  When  stimulated,  its  contractions  occur  slowly,  but  last  for 
a  considerable  length  of  time. 

Nonstriped  Muscle. — These  muscles  are  made  up  of  a  number  of 
contractile  fiber-cells  of  an  elongated,  fusiform  shape,  and  usually 
pointed  at  the  end.  These  fiber-cells  may  be  readily  demonstrated  by 
placing  the  tissue  in  a  strong  alkaline  solution  or  a  solution  of  strong 
nitric  acid. 

Upon  transverse  section  they  are  generally  prismatic,  but  some- 
timcs  are  more  flattened.  Their  muscle-substance  is  doubly  refract- 
ing. Each  cell  has  a  nucleus  which  is  either  elongated  or  oval.  It 
may  contain  one  or  more  nucleoli.  The  nucleus  is  brought  into  view 
by  means  of  dilute  acetic  acid  or  staining  reagents. 

The  involuntary  fiber-cells  have  a  delicate  sheath,  which,  like 
llic  sarcolemma  of  voluntary  muscle-fiber,  is  very  apt  to  become 
wrinkled  when  the  fiber  is  contracted.  By  reason  of  this  an  indis- 
tinctly striated  appearance  may  be  produced. 


368 


PHYSIOLOGY. 


While  fiber-cells  do  occur  singly,  yet  it  is  more  common  for  them 
to  be  found  in  groups.  Thus,  muscular  sheets,  or  bundles,  are  pro- 
duced which  may  cross  one  another  and  interlace,  being  held  in 
position  by  enveloping  connective  tissue.  The  individual  cells  are 
united  by  the  presence  of  a  very  delicate  cement. 

The  average  length  of  the  fiber-cells  ranges  from  yioo  to  1/o00 
inch;  those  forming  the  middle  coat  of  the  arteries  are  shorter,  those 


Fig.  85. — Unstriped  Muscular  Tissue.     (ELLENBERGER.) 

A  and  B,  Foetal  cells.     C,  H,  Fully  formed  fiber.     /,  Bundle  of  fibers. 

K,   Cross-section  of  bundle  of  pale  muscular  fibers. 

in  the  intestinal  tract  and  the   pregnant  uterus   are   considerably 
longer. 

WHERE  FOUND. — The  unstriped  muscular  tissue  is  more  generally 
distributed  within  the  body  than  one  would  suppose.  It  is  found  in 
the  lower  part  of  the  oesophagus,  in  the  stomach,  small  and  large 
intestines ;  in  arteries,  veins,  and  lymphatics ;  in  the  ureters,  bladder, 
and  urethra;  in  the  internal  female  generative  organs,  etc. 


THE  MUSCLES.  369 

BLOOD-SUPPLY. — The  blood-supply  to  unstriped  muscle  is  very 
free,  but  not  nearly  so  liberal  as  that  to  voluntary  muscle.  The  nerve- 
supply  is  from  the  sympathetic  system,  and  comprises  both  medullated 
and  nonmedullated  fibers.  The  fibers  form  a  main  plexus,  lying  in 
the  connective  tissue  of  the  perimysium.  From  this  plexus  of  fibers 
there  come  off  numerous  fibrils,  which  traverse  the  fiber  and  nucleus. 

Irritability  of  Muscle. — Contractility,  elasticity,  tonicity,  and 
irritability  are  terms  used  to  designate  various  properties  of  muscles. 

Thus,  contractility  is  the  property  the  muscle  possesses  of  short- 
ening and  of  giving  a  contraction  when  it  is  excited. 

Elasticity  is  the  general  property,  common  to  muscles  and  many 
other  bodies,  of  stretching  under  the  influence  of  a  weight  and  of 
then  returning,  more  or  less  perfectly,  to  the  first  shape. 

Tonicity  is  the  state  midway  between  extreme  contraction  and 
relaxation.  It  is  a  condition  depending  upon  the  central  nervous 
system. 

In  addition,  muscle  possesses  a  property  that  is  common  to  all 
live  tissues  and  which  is  of  fundamental  importance  in  general 
physiology.  It  is  irritability.  By  irritability  is  meant  that  property 
of  a  living  element  to  act  according  to  its  nature  under  the  stimulus 
of  an  excitant. 

Paralyses  have  been  observed  which  have  lasted  for  several 
months  or  even  several  years  and,  although  the  nerves  were  abso- 
lutely unexcitable,  yet  the  muscles  had  retained  their  irritability. 
This  may  be  readily  demonstrated  in  cases  of  paralysis  of  the  seventh 
pair  of  nerves. 

The  independence  of  muscle  irritability  is  formally  demonstrated 
by  experiment  in  which  the  known  action  of  the  drug,  curare,  upon 
muscles  is  taken  advantage  of.  A  watery  extract  of  this  drug,  when 
injected  into  the  blood  of  an  animal  or  introduced  beneath  its  skin, 
acts  chiefly  upon  the  motor  nerve-endings.  It  does  not,  however,  affect 
muscular  contractility.  Curare  is  an  agent  which  separates  the 
muscle-element  from  the  nerve-element  by  a  physiological  dissection 
much  superior  to  the  coarse  anatomical  dissections  which  we  could 
make. 

When  a  few  milligrams  of  this  drug  are  injected  into  the  dorsal 
lymph-sac  of  a  frog,  the  poison  is  absorbed  within  a  few  minutes. 
The  animal  soon  ceases  to  support  itself,  but  lies  in  any  position  in 
which  it  may  be  placed  by  the  experimenter.  It  is  paralyzed,  produc- 
ing neither  voluntary  nor  reflex  movements.  Now,  should  the  brain  be 
destroyed,  the  skin  removed,  and  the  sciatic  nerve  stimulated  by 


24 


370  PHYSIOLOGY. 

electricity,,  no  movements  of  the  muscles  of  the  limb  follow.  On  the 
other  hand,  should  the  stimulus  be  applied  directly  to  the  muscles, 
they  immediately  contract.  Therefore  the  muscle  is  irritable  by  itself. 

By  this  it  would  seem  to  be  clearly  demonstrated  that  irritability 
belongs  to  the  muscle,  and  does  not  depend  upon  the  nerve-fibers 
mingled  with  those  of  the  muscle. 

In  addition  to  this  classical  experiment  there  may  be  mentioned 
several  other  facts  which  go  to  corroborate  what  has  been  stated 
concerning  irritability : — 

1.  The  chemical  excitants  of  the  muscle  are  not  the  same  as  the 
chemical  excitants  of  the  nerves.    Thus,  glycerin  excites  the  nerve, 
but  has  no  effect  upon  the  muscle. 

2.  Isolated  muscle-fibers  have  been  seen  which,  according  to 
microscopical  examination,  contained  no  nervous  elements  and  which, 
notwithstanding,  were  contractile. 

3.  If  the  decreasing  progress  of  irritability  be  followed  after 
death,  in  the  muscle  as  well  as  in  the  nerve,  it  will  be  found  that  the 
nerve  dies  long  before  the  muscle.     When  the  nerves  have  lost  ail 
irritability,  the  muscle  is  still  alive,  and  can  contract  under  the  influ- 
ence of  excitations  directly  applied  to  its  tissue.    It  is  at  that  very 
moment  when  the  nerves  have  lost  all  excitability  that  the  muscle  is 
at  its  maximum  of  irritability. 

INFLUENCE  OF  BLOOD  UPON  IRRITABILITY. — It  has  been  demon- 
strated by  experiment  upon  the  frog  that  when  the  artery  of  a  mem- 
ber is  ligated  the  muscle  contraction  is  less  high  and  less  strong  than 
if  the  artery  had  been  left  intact. 

Stenon's  experiment  of  ligating  the  abdominal  aorta  of  a  dog 
is  worthy  of  mention.  In  twenty  to  thirty  minutes  after  the  ligation 
the  dog  seems  paraplegic.  He  is  unable  to  stand  upon  his  hind  limbs. 
Reflex  and  voluntary  movements  are  completely  lost;  muscle  irrita- 
bility,  however.,  persists  for  nearly  three  hours. 

When  the  ligature  is  removed  movement  does  not  return  to  the" 
limbs  at  once,  but  within  a  very  short  time  the  dog  is  able  to  stand 
upon  his  four  feet. 

Stimuli. — Those  extreme  forces  which  bring  into  play  the  irrita- 
bility of  the  muscle  are  simply  various  forms  of  energy.  To  them  the 
name  stimuli  has  been  applied.  By  their  action  the  muscle  is  thrown 
into  a  state  of  excitement  whereby  the  chemical  energy  of  the  muscle 
is  transformed  into  heat  and  work.  These  muscle  excitants,  or  stimuli, 
are  of  five  varieties:  (a)  nervous,  (b)  electrical,  (c)  thermal,  (d) 
mechanical,  and  (e)  chemical. 


THE  MUSCLES.  371 

NERVOUS  STIMULI. — The  most  important  of  all  the  excitatory 
forces  of  the  muscle  is  innervation.  In  the  normal  state  there  is 
scarcely  any  other  than  this  to  produce  muscle  contraction.  Our  mus- 
cles, as  well  as  those  of  all  other  animals,  contract  because  the  motor 
nerve  transmits  to  them  the  spontaneous  or  reflex  excitation  of  the 
nervous  centers.  The  nerve  impulses  average  about  ten  per  second. 
The  stimulus  is  exactly  proportioned  to  the  effect  which  must  be 
obtained. 

ELECTRICAL  STIMULI. — Electricity  is  employed  as  a  stimulus  in 
preference  to  any  other  external  agent  to  bring  into  play  the  irrita- 
bility of  muscle. 

THERMAL  STIMULI. — Thermic  excitations  also  provoke  muscular 
movements.  The  stomach  and  intestines  are  viscera  whose  muscles 
are  very  readily  excited  by  heat  and  cold.  They  contract  very  ener- 
getically when  very  cold  drinks  are  taken  and  their  temperature  sud- 
denly modified.  On  the  contrary,  striated  muscles  hardly  react  to 
thermic  excitants.  If  heat  or  cold  be  applied  gradually,  there  is  not 
produced  any  muscle  contraction.  Excitants  act  only  when  they  are 
applied  suddenly. 

MECHANICAL  STIMULI. — Mechanical  excitants  that  are  capable  of 
producing  muscular  contraction  are  rather  common.  Thus,  the 
surgeon,  while  performing  an  operation,  notices  slight  fibrillary 
tremblings  following  each  stroke  of  his  scalpel. 

CHEMICAL  STIMULI. — It  can  be  stated  as  a  rule  that  all  the  sub- 
stances which  are  fatal  to  the  life  of  the  muscle  are  excitants  of  the 
muscle.  On  this  ground,  distilled  water  is  an  excitant,  for  when  it  is 
injected  into  the  arterial  system  of  a  frog  its  muscles  show  fibrillary 
twitchings.  Not  only  does  the  water  excite  the  muscle,  but  it  also 
kills  rapidly. 

Chemical  Constitution  of  Muscle-tissue. — The  chemical  study  of 
muscle  is  one  of  the  most  difficult  of  physiological  chemistry.  There 
are  in  the  muscle  proteid  matters  which  are  very  like  one  another  and 
which  can  be  distinguished  only  by  superficial  characters.  This  ren- 
ders results  far  from  being  satisfactory  or  reliable. 

Besides,  it  is  necessary,  in  order  to  know  chemical  reactions  of 
muscles,  to  study  only  living  muscle.  But  from  previous  study  it  will 
be  recalled  that  even  the  weakest  chemical  actions  produce  very  de- 
cided changes  in  the  muscle,  with  consequent  alteration  of  its  chem- 
ical functions. 

Then,  too,  muscle-fiber  is  mingled  with  many  other  tissues,  ar- 
teries, veins,  nerves,  connective  tissue,  etc.;  the  separation  of  the 


372  PHYSIOLOGY. 

muscular  fiber  from  its  enveloping  media  is  almost  impossible  com- 
pletely to  effect. 

Reaction. — Living  muscle  is  alkaline;  however,  after  extreme 
activity  and  after  death  its  reaction  is  found  to  be  acid.  This  is  due 
to  the  development  of  sarco-lactic  acid.  The  postmortem  change  in 
muscular  constitution  is  due  to  spontaneous  coagulation  of  a  proteid 
within  the  muscle-fibers. 

Among  the  constituent  substances  of  the  muscle-fiber  are  dis- 
tinguished: (1)  proteids — myosinogen,  myo-albumin,  my o globulin; 
(2)  glycogen;  (3)  ferments  and  mineral  salts;  (4)  extractives. 

PROTEIDS.  —  The  sarcolemma  of  the  muscular  fiber  resembles 
elastin  very  closely  as  to  its  solubilities.  Within  the  soft,  contracting 
portion,  the  sarcous  substance,  is  a  large  percentage  of  proteids  and 
smaller  proportions  of  extractives  and  salts. 

Myosin  is  formed  from  myosinogen,  myosin  ferment,  and  calcium 
salts. 

Syntonin. — When  a  solution  of  myosin  is  heated  it  is  altered  in 
such  a  manner  that  it  can  no  longer  be  dissolved  in  NaCl  as  before. 

If  it  be  treated  with  dilute  HC1,  it  becomes  altered  in  still  another 
manner,  and  produces  an  important  substance  which  is  called  syntonin. 

If  syntonin  in  HC1  solution  have  pepsin  added  to  it,  the  syntonin 
is  transformed  into  peptone. 

Muscle-serum. — It  will  be  remembered  that  in  the  coagulation  of 
blood  two  principal  components  were  noted :  the  clot  and  the  serum 
floating  upon  the  clot.  Also,  after  coagulation  of  the  muscular  juice, 
myosin  and  serum  must  be  distinguished. 

The  muscle-serum  which  floats  upon  the  surface  of  the  myosin 
contains  several  substances.  Among  them  the  chemist  points  out  two 
principal  ones:  myo-albumin  and  myoglobulin. 

In  that  part  of  the  muscle  which  does  not  yield  muscle-juice 
there  are  insoluble  albumins.  They  are  rich  in  nuclein. 

The  amount  of  proteid  matters  contained  in  the  muscular  tissues 
is  very  variable.  It  is  usually  stated  that  in  100  parts,  by  weight,  of 
muscle,  there  are  20  parts  of  proteid  matters. 

Myolicematin. — Another  proteid  found  within  the  muscle  is  myo- 
hsematin.  It  is  the  coloring  matter  of  muscle. 

EXTRACTIVES. — Creatinin  is  found  in  nearly  all  muscles.  Cre- 
atinin  is  derived  from  creatin  by  dehydration.  The  amount  of 
creatinin  in  muscle  is  small,  being  but  0.2  per  cent. 

Muscle  also  contains  the  purin  bodies :  hypoxanthin  and  xanthin. 
These  bodies  occur  to  the  extent  of  about  0.02  per  cent. 


THE  MUSCLES.  373 

There  is  in  muscle-juice  a  substance  analogous  to  pepsin.  When  a 
muscle  becomes  acid  in  reaction  and  the  temperature  is  suitable,  the 
pepsin  acts  upon  the  proteids  to  convert  them  into  albumoses  and 
peptones. 

Halliburton  found  a  my 'osin- ferment.  Its  presence  would  seem 
to  explain  the  coagulation  of  myosin. 

GLYCOGEN. — Among  the  nonnitrogenized  substances  must  first  be 
classed  the  sugars  and  their  analogues.  Glycogen  is  the  principal 
muscle-starch.  The  glycogen  in  the  muscles  was  discovered  by  Claude 
Bernard  while  looking  for  the  glycogen  in  the  liver  of  the  foetus  and 
newborn.  He  found  in  the  muscles  of  the  embryo  quantities  of 
glycogen  that  were  relatively  enormous.  Glycogen  exists  in  all  of  the 
muscles. 

The  more  active  the  state  of  a  muscle,,  the  less  glycogen  it  con- 
tains. Therefore,  much  of  it  is  found  in  those  muscles  which  contract 
but  little. 

Muscle  extract  and  pancreatic  extract  obtained  by  expression 
when  mixed  together  rapidly  destroy  sugar,  probably  by  the  formation 
of  a  ferment.  Either  extract  alone  is  powerless  to  break  up  glucose. 
These  two  extracts  resemble  the  action  of  enterokinase  upon  trypsin- 
ogen  and  explain  the  diabetes  due  to  removal  of  the  pancreas. 

INOSITE. — Another  sugarlike  matter  has  been  found  in  the  mus- 
cle-fiber. It  is  inosite.  It  is  a  sort  of  crystallizable  body  that  is  un- 
fermentable.  That  is,  it  does  not  ferment  to  form  alcohol,  but  lactic 
acid.  It  is  found  in  the  vegetable  kingdom  also,  where  it  is  usually 
extracted  from  peas  or  beans.  It  is  identical  with  the  inosite  of 
muscle.  It  is  not  a  sugar,  but  belongs  to  the  aromatic  series. 

FATS. — Muscle  also  contains  fats. 

MINEKAL  SUBSTANCES. — Alkaline  phosphates  predominate.  In 
100  parts  of  ash  there  are  about  90  parts  of  phosphates.  The 
metals  found  in  muscle  are :  Potassium,  sodium,  and  calcium ;  there 
is  also  a  small  quantity  of  magnesium  and  iron.  Phosphoric  acid 
exists  in  muscle  as  inorganic  phosphates,  phosphorus  of  phospho- 
carnic  acid,  and  phosphorus  of  inosinic  acid.  Carnic  acid  is  identical 
with  antipeptone.  When  a  muscle  works  it  increases  the  phosphates 
in  the  urine.  The  gases  found  in  muscle  are  carbonic-acid  gas  and 
oxygen. 

Adipocere  is  a  waxy  substance  which  replaces  muscular  tissue  if 
bodies  be  buried  in  damp  soil.  It  consists  principally  of  a  soap  made 
of  calcium  with  palmitic  and  stearic  acids. 


374 


PHYSIOLOGY. 


Fig.  86. — The  Pendulum  Myograph.      (FOSTER.) 

A,  Smoked  glass  plate,  swings  on  the  "seconds"  pendulum,  B,  by  means  of  carefully 
adjusted  bearings  at  C.  The  contrivances  by  which  the  glass  plate  can  be  moved  and 
replaced  at  pleasure  are  not  shown.  A  second  glass  plate,  so  arranged  that  the  first 
glass  plate  may  be  moved  up  and  down  without  altering  the  swing  of  the  pendulum, 


THE  MUSCLES.  375 

Rigor  Mortis. — That  state  of  firmness,  of  retraction,  and  of  stiff- 
ness in  which  the  limbs  of  an  animal  are  found  some  time  after  death 
is  called  rigor  mortis.  It  is  caused  by  the  coagulation  of  the  myo- 
sinogcn. 

In  man  it  is  generally  four  hours  after  death  that  cadaveric  rigid- 
ity becomes  complete.  As  a  rule,  it  may  be  said  that  rigidity  begins 
two  hours  after  death,  reaching  its  maximum  two  hours  later. 

A  particular  kind  of  rigor  mortis  has  been  observed  by  military 
surgeons.  Soldiers  while  in  full  activity  have  been  struck  by  pro- 
jectiles and  have  been  seen  to  become  stiff  instantaneously.  It  is  a 
sort  of  rigor  mortis  which  seizes  all  of  the  muscles  of  the  body  im- 
mediately after  death. 

Influence  of  Temperature. — Animals  which  have  died  in  heated 
chambers  become  rigid  very  quickly  and  the  rigidity  disappears  as 
quickly. 

Cold,  which  retards  chemical  phenomena,  retards  the  appearance 
of  cadaveric  rigidity  and  prolongs  it  enormously. 

Influence  of  Fatigue- — The  influence  of  prolonged  labor  of  the 
muscle  upon  the  premature  appearance  of  rigidity  is  an  indisputable 
fact. 

MUSCULAR  LABOR  AND  UREA  EXCRETION. — The  amount  of  urea 
excreted  from  the  body  is  not  markedly  increased  during  muscular 
labor. 

LACTIC  ACID. — The  production  of  lactic  acid  is  the  more  abun- 
dant as  the  muscle  has  been  longer  and  more  strongly  excited. 

Myograph. — The  du  Bois-Eeymond  induction  coil  is  the  one  most 
commonly  employed  in  physiological  experiments.  When  it  is  neces- 
sary to  use  very  rapid  breaking  of  the  current,  some  instrument  must 

is  also  omitted.  Before  commencing  an  experiment  the  pendulum  is  raised  up  (in  the 
figure  to  the  right)  and  is  kept  in  that  position  by  the  tooth  (a)  catching  on  the  spring- 
catch  (6).  On  depressing  the  catch  (6)  the  glass  plate  is  set  free,  swings  into  the  new 
position  indicated  by  the  dotted  lines,  and  is  held  in  that  position  by  the  tooth  (a') 
catching  on  the  catch  (&')•  In  the  course  of  its  swing  the  tooth  (a'),  coming  into  con- 
tact with  the  projecting  steel  rod  (c),  knocks  it  on  one  side  into  the  position  indicated 
by  the  dotted  line  (c').  The  rod  (c)  is  in  electrical  continuity  with  the  wire  (x)  of  the 
primary  coil  of  an  induction-machine.  The  screw  (d)  is  similarly  in  electrical  continuity 
with  the  wire  (y)  of  the  same  primary  coil.  The  screw  (d)  and  the  rod  (c)  are  armed 
with  platinum  at  the  points  at  which  they  are  in  contact,  and  both  are  insulated  by 
means  of  the  ebonite  block  (e).  As  long  as  c  and  d  are  in  contact  the  circuit  of  the 
primary  coil  to  which  x  and  y  belong  is  closed.  When  in  its  swing  the  tooth  (a,')  knocks 
c  away  from  d,  at  that  instant  the  circuit  is  broken,  and  a  "  breaking  "  shock  is  sent 
through  the  electrodes  connected  with  the  secondary  coil  of  the  machine  and  so  through 
the  nerve.  The  lever  (I),  the  end  only  of  which  is  shown  in  the  figure,  is  brought  to 
bear  on  the  glass  plate,  and  when  at  rest  describes  a  straight  line,  or  more  exactly  an 
arc  of  a  circle  of  large  radius.  The  tuning-fork  (f),  the  ends  only  of  the  two  limbs 
of  which  are  shown  in  the  figure  placed  immediately  below  the  lever,  serves  to  mark 
the  time. 


376 


PHYSIOLOGY. 


be  employed  for  that  purpose.  The  first  instrument  used  in  making 
myograms  was  that  of  Helmholtz. 

Simple  Contraction. — If  a  single  induction  shock  be  applied  to 
a  muscle  there  will  result  a  simple  muscular  contraction ;  that  is,  the 
muscle  responded  by  a  quick  contraction,  with  return  to  its  former 
relaxed  condition.  This  contraction,  when  graphically  shown,  is 
termed  a  simple  muscle-curve. 

MUSCLE-CURVE,  OR  MYOGRAM. — If  the  muscle-curve  of  a  single 
stimulus  be  analyzed,  it  will  be  seen  to  be  composed  of  various  ele- 
ments, as  follows:  (1)  period  of  latent  stimulation,  (2)  period  of 
contraction,,  and  (3)  period  of  relaxation. 


a  b 


Fig.  87. — A  Muscle-curve  Obtained  by  Means  of  the  Pendulum 
Myograph.     (  FOSTER.) 

To  be  read  from  left  to  right. 

a  indicates  the  moment  at  which  the  induction-shock  is  sent  into  the 
nerve.  6,  The  commencement;  c,  the  maximum;  and  d,  the  close  of  the 
contraction.  The  two  smaller  curves  succeeding  the  larger  one  are  due  to 
oscillations  of  the  lever. 

Below  the  muscle-curve  is  the  curve  drawn  by  a  tuning-fork  making  180 
double  vibrations  a  second,  each  complete  curve  therefore  representing  Viso 
of  a  second.  It  will  be  observed  that  the  plate  of  the  myograph  was  traveling 
more  rapidly  toward  the  close  than  at  the  beginning  of  the  contraction,  as 
shown  by  the  greater  length  of  the  vibration-curves. 

Latent  Period. — The  significance  of  this  term  is  that  the  muscle 
experimented  with  does  not  respond  at  the  precise  moment  when  the 
stimulus  is  applied  to  it.  The  response  comes  later — about  1/100  of  a 
second.  During  the  latent  period  there  is  no  apparent  change  oc- 
curring within  the  muscle.  The  latent  period  may  be  modified  by 
increased  stimulus  and  heat,  when  it  becomes  shortened ;  fatigue  and 
cold  lengthen  the  time.  The  latent  period  of  unstriped  muscle  may 
be  as  long  as  one  or  two  seconds. 

Contraction  Period. — The  muscle-curve  comprises  two  periods: 
that  of  the  ascent  and  that  of  the  descent  of  the  muscle.  The  ascent 
of  the  curve  represents  the  contraction  of  the  muscle  until  it  has 


THE  MUSCLES. 


377 


reached  its  maximum.  The  rate  of  contraction  is  at  first  a  trifle  slow, 
then  more  rapid  and  more  slow  a  second  time.  The  extent  is  */100 
of  a  second. 

Relaxation  Period. — After  the  muscle  has  contracted  to  its  max- 
imum, it  begins  to  relax — at  first  slowly,  then  more  quickly,  and 
finally  more  slowly  again.  Its  duration  is  5/100  of  a  second.  It  is 
shorter  with  a  weak  stimulus  and  longer  with  a  strong  stimulus. 

In  the  myograph  we  use  a  light  lever  and  a  weight  as  near  its 
axis  as  possible  to  record  the  contraction.  Here  the  tension  of  the 


Fig.  88. — Arrangement  of  Apparatus  in  Conducting  Experiments  on 
Nerve  and  Muscle.     (STIRLING.) 

B,  Galvanic  battery.  K,  Electric  key  in  primary  circuit.  P,  primary  coil 
of  induction  machine.  8,  Secondary  coil  of  induction  apparatus,  from  which 
the  current  is  conducted  when  the  key  (K')  is  open  to  the  electrode  (E)  on 
which  rests  the  nerve  (n).  The  muscle  (M)  is  supported  by  a  clamp  under 
a  glass  shade,  its  tendon  being  connected  by  a  thread  with  a  lever  (L)  writ- 
ing on  the  smoked  surface  of  a  revolving  drum.  The  time-marker  (TM)  is 
included  in  the  primary  circuit  so  that  when  the  current  passes  through  P  by 
closing  the  key  (K)  it  also  traverses  the  electromagnet  of  the  time-marker 
and  causes  a  record  of  the  instant  of  stimulation  to  be  made  on  the  surface 
of  the  drum.  8,  Stand  supporting  moist  chamber.  TF,  Weight  by  which 
muscle  is  stretched  and  which  is  lifted  in  the  contraction  of  the  muscle. 

muscle  in  its  contraction  and  relaxation  remains  nearly  the  same. 
This  contraction  is  called  an  isotonic  contraction.  The  isometric 
contraction  is  produced  when  the  muscle  pulls  against  a  spring.  Here 
the  muscle  undergoes  slight  change  in  length  and  the  energy  of 
change  of  form  is  transformed  into  tension  and  stored  in  the  spring. 
An  examination  of  isometric  and  isotonic  curves  proves  that  a  muscle 
which  has  shortened  to  a  given  length  will  be  making  a  far  greater 
pull  when  its  effort  to  shorten  has  been  resisted  than  when  it  has 


378 


PHYSIOLOGY. 


reached  the  same  during  a  contraction  without  resistance,  which  is 
an  isotonic  contraction. 


CURVE  OF  FATIGUE. — When  a  muscle  has  become  fatigued  and 
its  myogram  studied,  at  first  the  contractions  improve  for  a  short 
time.  This  is  shown  by  the  successive  contractions  being  higher. 


THE  MUSCLES. 


379 


Afterward'  the  latent  period  increases,  the  curve  becomes  less  high, 
while  the  contraction  becomes  slower  and  lasts  longer.  The  resultant 
myogram  gives  the  picture  spoken  of  as  the  "staircase." 

Veratrine  and  adrenalin  greatly  prolong  the  stage  of  relaxation 
in  a  muscle. 

BESTING  AND  ACTING  MUSCLE. — The  chief  differences  between 
resting  and  acting  muscle  are:  (1)  the  acting  muscle  forms  more 
C02;  (2)  more  oxygen  is  consumed;  (3)  sarco-lactic  acid  is  formed; 
(4)  glycogen  is  made  use  of;  (5)  the  substances  soluble  in  water 
diminish  in  amount,  while  those  soluble  in  alcohol  increase. 

CHANGES  IN  THE  VOLUME  or  THE  MUSCLE  DURING  CONTRAC- 
TION.— Muscular  contraction  can  be  defined  by  its  apparent  effects: 
a  shortening  of  the  muscle.  By  experiment  it  has  been  shown  that 


Fig.  90. — Tracing  of  a  Double  Muscle-curve.     (FOSTER.) 

To  be  read  from  left  to  right. 

While  the  muscle  was  engaged  in  the  first  contraction  (whose  complete 
course,  had  nothing  intervened,  is  indicated  by  the  dotted  line),  a  second 
induction  shock  was  thrown  in  at  such  time  that  the  second  contraction 
began  just  as  the  first  was  beginning  to  decline.  The  second  curve  is  seen 
to  start  from  the  first  as  does  the  first  from  the  base  line. 

the  muscle  on  contracting  simply  shifts  its  muscular  units  when  it 
shortens,  for  the  volume  of  the  muscle  remains  the  same.  The 
velocity  of  a  contraction-wave  in  muscle  can  be  measured ;  in  the  frog 
it  is  from  three  to  four  meters  per  second;  in  man,  about  forty  -feet  per 
second. 

The  Effects  of  Two  Successive  Stimuli. — Let  the  student  imagine 
two  successive  momentary  stimuli  applied  successively  to  a  muscle. 
The  stimuli  may  be  either  maximal  or  submaximal;  that  is,  either  the 
greatest  possible  contraction  the  muscle  is  able  to  accomplish  or  only 
a  medium  contraction  from  the  applied  stimulus. 

If  each  of  the  two  stimuli  be  maximal,  the  effects  produced  will 
vary  according  to  the  time  of  application  of  the  two  excitants.  Thus, 
(1)  if  the  second  stimulus  be  applied  after  the  relaxation  following 
the  effect  of  the  first  stimulus,  then  the  myogram  shows  two  maximal 


380  PHYSIOLOGY. 

contractions;  (2)  if  the  second  stimulus  follow  the  first  with  such 
rapidity  that  the  two  occur  during  the  latent  period  of  the  muscle- 
curve,  then  the  recording  instrument  shows  but  one  maximal  con- 
traction. 

If  the  two  stimuli  be  nonmaximal,  the  effects  of  the  two  separate 
stimuli  will  be  superimposed;  that  is,  there  will  be  a  summation  of 
the  contractions.  This  summation  occurs  regardless  of  the  time  of 
application  of  the  stimuli. 

Summation  of  Stimuli. — As  the  second  stimulation  was  just  seen 
to  add  its  curve  to  the  first,  so  does  the  third  add  itself  to  the  second, 
the  fourth  to  the  third,  etc.  If  the  excitations  occur  with  a  rhythm 
that  is  not  too  rapid,  the  various  shocks  are  nearly  equal,  as  shown 
by  the  myogram,  but  yet  they  do  not  mingle.  These  isolated  shocks 
are  seen  when  the  rhythm  does  not  exceed  six  per  second. 


\ 


a, 

Fig.  91. — Tetanus  Produced  with  the  Ordinary  Magnetic  Interrupter  of  an 
Induction  Machine.     (Recording  surface  traveling  slowly.)     (FOSTER.) 

To  be  read  from  left  to  right. 

The  interrupted  current  being  thrown  in  at  a,  the  lever  rises  rapidly; 
but  at  6  the  muscle  reaches  the  maximum  of  contraction.  This  is  continued 
till  c,  when  the  current  is  shut  off  and  relaxation  commences. 

If,  now,  these  same  excitations  be  repeated  with  a  frequency  of 
twenty  per  second,  isolated  shocks  will  not  be  seen.  Each  stimulus, 
lasting  but  1/20  of  a  second,  does  not  allow  the  muscle  completely  to 
relax;  thus,  the  second  contraction  encroaches  upon  the  first,  the 
third  upon  the  second,  etc.  From  the  rapid  succession  of  the  stimuli, 
the  muscle  remains  in  a  condition  of  continued  vibratory  contraction. 
That  is,  in  a  state  of  tetanus. 

Complete  Tetanus, — If  the  excitation  rhythm  be  more  frequent,— 
say,  fifty  of  them  per  second, — there  will  no  longer  be  any  trace  of 
the  primitive  shocks.  The  ascent  of  the  muscle-curve  will  be  abrupt 
and  decided;  the  contraction  due  to  the  first  shock  will  not  be  fol- 
lowed by  any  relaxation.  There  will  be  no  oscillation  recorded  upon 
the  myogram.  The  upper  straight  line  due  to  the  complete  contrac- 
tion of  the  muscle  is  called  the  plateau.  When  the  muscle  is  in  this 
condition  the  tetanus  is  said  to  be  perfect  or  complete. 


THE  MUSCLES. 


381 


The  tetanus  is  spoken  of  as  incomplete  when  there  are  still  relax- 
ations and  vibrations  which  indicate  the  incomplete  mingling  of  the 
shocks. 

The  number  of  stimuli  that  are  required  to  produce  tetanus  may 
be  very  variable.  Fifteen  to  twenty  stimuli  per  second  suffice  to 
throw  a  frog's  muscle  into  tetanus. 


Fig.  92. — Muscle  Thrown  into  Tetanus,  when  the  Primary  Current  of  an 
Induction  Machine  is  Repeatedly  Broken  at  the  Rate  of  Sixteen 
„     Times  per  Second.  (FOSTER.) 

To  be  read  from  left  to  right. 

The  upper  line  is  that  described  by  the  muscle.  The  lower  marks  time, 
the  intervals  between  the  elevations  indicating  seconds.  The  intermediate 
line  shows  when  the  shocks  were  sent  in,  each  mark  on  it  corresponding  to 
a  shock.  The  lever,  which  describes  a  straight  line  before  the  shocks  are 
allowed  to  fall  into  the  nerve,  rises  almost  vertically  (the  recording  surface 
traveling  in  this  case  slowly)  as  soon  as  the  first  shock  enters  the  nerve  at  a. 
Having  risen  to  a  certain  height,  it  begins  to  fall  again,  but  in  its  fall  is 
raised  once  more  by  the  second  shock,  and  that  to  a  greater  height  than  be- 
fore. The  third  and  succeeding  shocks  have  similar  effects,  the  muscle  con- 
tinuing to  become  shorter,  though  the  shortening  at  each  shock  is  less. 
After  a  while  the  increase  in  the  total  shortening  of  the  muscle,  though  the 
individual  contractions  are  still  visible,  almost  ceases.  At  6  the  shocks  cease 
to  be  sent  into  the  nerve;  the  contractions  almost  immediately  disappear, 
and  the  lever  forthwith  commences  to  descend.  The  muscle  being  lightly 
loaded,  the  descent  is  very  gradual;  the  muscle  had  not  regained  its  natural 
length  when  the  tracing  was  stopped. 

DURATION  OF  TETANUS. — A  tetanized  muscle  cannot  be  kept  con- 
tracted for  a  considerable  length  of  time,  even  though  the  stimuli 
be  kept  constant.  The  muscle  begins  to  elongate — at  first  somewhat 
quickly,  but  later  more  slowly.  This  change  is  produced  by  fatigue 
of  the  muscle. 

Muscle-sound.  —  Helmholtz  said  that  36  vibrations  per  second 
formed  the  average  for  the  production  of  muscular  tones.  To-day 
this  is  considered  an  overtone,  and  the  requisite  number  of  necessary 
vibrations  is  placed  at  19  per  second. 


382  PHYSIOLOGY. 

FIRST  HEART-SOUND. — It  is  probable  that  the  first  sound  of  the 
heart  is  partly  a  muscle-sound.  It  is  a  dull  sound,  persisting  when 
the  thorax  is  taken  away  and  the  auriculo-ventricular.  valves  are  de- 
stroyed. The  sound  could  not  in  such  an  instance  be  produced  by 
the  vibration  of  the  valves. 

Voluntary  Contraction. — The  number  of  single  impulses  sent  to 
our  muscles  during  voluntary  movements  are  somewhat  variable. 
There  are  from  8  to  12  impulses  for  a  slow  movement  and  from  18  to 
20  impulses  per  second  for  a  rapid  movement.  Ten  vibrations  per 
second  may  be  taken  as  the  average. 

Elasticity  of  the  Muscle. — 01  all  the  properties  of  muscle,  elas- 
ticity is  the  one  least  well  known,  the  one  which  is  most  difficult  to 
explain  and  understand. 

Physicists  say  that  a  body  is  perfectly  elastic  when,  after  having 
been  removed  from  its  first  position,  it  returns  exactly  to  the  orig- 
inal position.  Thus,  an  ivory  ball  is  perfectly  elastic;  after  it  has 
been  flattened  by  an  external  force  it  returns  exactly  to  its  original 
shape. 

If  a  piece  of  rubber  is  stretched  by  adding  successive  weights  it 
is  found  that  the  series  of  elongations  are  nearly  proportional  to  the 
weights.  When  the  weights  are  successively  removed  it  will  be  found 
that  the  elasticity  of  the  rubber  is  nearly  perfect.  But  if  over- 
weighted for  a  long  time  it  does  not  return  completely  to  its  original 
length,  and  the  elasticity  disappears  gradually.  If  now  you  take  a 
frog's  fresh  muscle  and  successively  load  it,  the  extension  of  the  muscle 
for  each  weight  is  not  proportional  to  the  weight  used,  but  with  each 
increase  in  weight  the  muscle  stretches  rather  less,  the  greater  the 
previous  extension.  On  removing  the  weights  the  muscle  shortens, 
but  it 'does  not  return  to  its  original  length.  A  contracted  muscle 
is  more  extensible  than  a  resting  one,  which  prevents  a  rupture  of 
the  muscle  in  a  sudden  contraction. 

Muscular  Work. — While  treating  of  elasticity  and  its  modifica- 
tion, tonicity,  it  might  be  well  to  give  a  brief  discussion  upon  muscular 
work.  The  amount  of  mechanical  work  which  a  muscle  performs 
equals  the  product  of  the  weight  lifted  and  the  height  to  which  the 
weight  is  lifted.  Thus,  the  work  =  height  X  the  weight. 

When  a  muscle  begins  to  contract,  it  is  then  that  it  lifts  the 
greatest  load;  as  the  contraction  continues,  the  muscle  is  capable  of 
lifting  less  and  less. 

If  the  height  be  expressed  in  feet  and  the  weight  in  pounds,  then 
the  work  performed  is  measured  in  units  of  foot-pounds.  Likewise, 


THE  MUSCLES.  383 

should  the  height  be  measured  in  meters  and  the  weight  in  grams, 
then  the  work  done  is  expressed  in  grammeters. 

In  studying  the  heights  of  contraction  in  a  loaded  muscle  it  is 
found  that  the  heights  of  lift  continuously  diminish,  but  the  actual 
work  done  by  the  muscle  increases  rapidly  and  then  more  slowly  until 
it  reaches  its  maximum  with  a  load  of  200  grams.  After  that  point 
the  work  done  slowly  decreases  and  then  more  rapidly  until  it  receives 
a  load  of  700  grams,  when  the  muscle  is  unable  to  contract. 

Dynamometer. — The  common,  clinical  form  of  dynamometer  is 
much  used  to  determine  the  absolute  force  of  certain  muscles.  The 
instrument  is  very  useful  to  determine  the  difference  in  grip  between 
the  two  hands  in  cases  of  paralysis.  The  patient  grasps  the  instru- 
ment in  his  hand  and  squeezes  upon  it;  the  power  exerted  is  regis- 
tered in  kilograms. 

Muscles  are  Most  Perfect  Machines. — They  take  the  best  ad- 
vantage of  the  fuel  supplied  to  them  and  give  in  return  a  very  high 
percentage  of  energy  in  the  form  of  work.  They,  by  legitimate  exer- 
cise, increase  in  strength  and  power  so  that  they  progressively  per- 
form more  work. 

The  steam  engine,  to  which  muscles  are  frequently  compared,  is 
inferior  in  every  respect.  The  best  made  steam  engine  shows  as 
work  only  about  12  per  cent,  of  the  total  energy  supplied  to  it  by  the 
oxidation  of  the  coal,  while  about  88  per  cent,  is  transformed  into 
heat.  Muscle  transforms  25  per  cent,  of  its  energy  into  work  and  75 
per  cent,  into  heat  to  warm  itself. 


CHAPTER  XII. 

VOICE   AND   SPEECH. 

IT  has  long  been  established  that  the  sounds  of  the  voice  in  man 
and  mammalia  are  produced  by  the  vibratory  action  of  the  vocal  cords. 
It  is  usually  the  blast  of  expired  air — under  certain  circumstances  the 
inspiratory  blast  also — in  its  passage  through  the  glottis  that  causes 
the  tense  vocal  cords  to  vibrate.  These  cords  vibrate  according  to 
the  laws  which  regulate  the  vibration  of  stretched  membranous  tongues. 
As  a  result  of  these  vibrations  sound  is  produced  which,  in  man,  is 
capable  of  being  so  modified  as  to  constitute  articulate  speech. 

Experiments  upon  living  animals  show  that  the  vocal  cords  are 
alone  the  essential  factors  in  the  production  of  sound.  For,  so  long 
as  these  remain  untouched,  although  all  other  parts  in  the  interior  of 
the  larynx  are  destroyed,  the  animal  is  still  able  to  emit  vocal  sounds. 

The  existence  of  an  opening  in  the  larynx  of  a  living  animal,  or 
of  man,  above  the  glottis  in  no  way  prevents  the  formation  of  vocal 
sounds;  however,  should  such  an  opening  occur  in  the  trachea,  it 
causes  total  loss  of  voice.  By  simply  closing  the  opening  sounds  can 
be  again  produced.  Such  openings  in  man  are  usually  met  with  as 
the  result  of  accident,  of  suicidal  attempts,  or  of  operations  performed 
upon  the  larynx  or  trachea  for  the  relief  of  disease. 

Production  and  Modification  of  Sounds. — Whenever  a  solid  body 
surrounded  by  air  is  thrown  into  vibration  the  sensation  of  sound  is 
carried  to  the  ear.  The  vibrations  must,  however,  be  of  certain 
strength  and  follow  one  another  with  certain  rapidity.  It  is  usually 
stated  that  if  the  vibrations  be  fewer  than  32  or  exceed  33,768  per 
second  n.o  effect  is  produced  upon  the  nerve  of  hearing. 

For  the  production  of  a  musical  sound  the  vibrations  must  suc- 
ceed each  other  at  regular  intervals;  if  the  vibrations  occur  at 
irregular  intervals,  only  a  noise  results. 

The  pitch  of  a  sound  depends  upon  the  number  of  vibrations 
within  a  given  period  of  time.  The  pitch  becomes  higher  in  direct 
proportion  to  the  rate  of  increase  in  the  rapidity  of  the  vibrations. 

The  strength,  or  intensity.,  of  the  sound  depends  upon  the  extent 
of  the  vibratory  action  of  the  sonorous  body. 
(384) 


VOICE  AND  SPEECH.  385 

Tone.,  or  timbre,  is  that  peculiar  character  of  a  musical  note 
whereby  it  can  at  once  be  distinguished  from  another  note  of  exactly 
the  same  pitch  and  strength. 

THE  ORGAN  OF  VOICE. 

The  special  organ  of  voice  in  man  is  that  portion  of  the  air- 
passages  called  the  larynx.  It  is  a  sort  of  hollow  chamber  which 
extends  from  near  the  root  of  the  tongue  to  the  first  ring  of  the 
trachea.  It  is  placed  in  the  middle  line  of  the  neck,  where  it  forms 
a  considerable  projection,  larger  above  than  below. 

Although  the  larynx  is  the  proper  organ  of  voice,  yet  the  lungs 
and  the  moving  parts  of  the  thorax  serve  to  propel  the  air  through  this 


Fig.  93. — The  Larynx  as  Seen  with  the  Laryngoscope.     (LANDOIS.) 

L.,  Tongue.  E.,  Epiglottis.  V.,  Vallecula.  R.,  Glottis.  L.  v.,  True  vocal 
cords.  8.  M.,^Sinus  Morgagni.  L.  v.  s.,  False  vocal  cords.  P.,  Position  of 
pharynx.  8.,  Cartilage  of  Santorini.  W.,  Cartilage  of  Wrisberg.  S.p.,  Sinus 
pyriformis. 

organ.  The  cavities  above  it,  including  the  pharynx,  mouth,  and 
nasal  cavities,  assist  in  modifying  the  vocal  sounds.  They  are,  there- 
fore, adjunct  organs  of  voice. 

Anatomy  of  the  Larynx. — The  larynx  consists  of  a  cartilaginous 
skeleton  which  constitutes  its  walls;  also  vocal  cords;  muscles  which 
move  directly  the  cartilaginous  pieces,  and  influence  indirectly  the 
tension  of  the  cords;  and,  finally,  a  mucous  membrane  which  lines 
the  internal  cavity. 

CARTILAGES. — The  cartilages  of  the  lar}rnx  are  four  in  number: 
two  unlike  and  two  alike.  One  of  the  former  is  inferior  and  exists 
in  the  form  of  a  signet-ring.  It  is  the  cricoid.  This  cartilage  is 
continuous  with  the  rings  of  the  trachea.  Its  narrower  portion  is 
situated  anteriorly;  its  wider  portion  is  placed  posteriorly.  It  ar- 


oSo 

ticulates  with  the  inferior  cornua  of  the  thyroid  cartilage,  forming 
the  crico-thyroid  articulation. 

The  other  odd  cartilage,  the  superior  one.  is  called  the  thyroid. 
It  is  composed  of  two  quadrilateral  lamina1  which  meet  in  front 
at  an  angle.  This  projection  is  popularly  known  as  Adam's  apple. 
Each  thyroid  lamina  terminates  posteriorly  in  two  horns  :  one  superior, 
the  other  inferior. 

The  two  cartilages  which  are  alike  are  the  arytenoids.  Each 
one  is  in  the  form  of  a  triangular  pyramid,  whose  base  is  movably 
articulated  at  the  back  on  the  cricoid  cartilage.  The  apex  of  each 
arytenoid  cartilage  has  attached  to  it,  in  the  shape  of  a  movable  point, 
a  cartilage  of  Santorini. 


Fig.  94.— Action  of  the  Muscles  of  the  Larynx.     (BEAUNIS.) 

The  dotted  line  indicates  the  new 'positions  assumed  by  the  thyroid  carti- 
lage in  the  action  of  the  crico-thyroid  muscle.  1,  Cricoid  cartilage.  2, 
Arytenoid  cartilage.  3,  Thyroid  cartilage.  4,  True  vocal  cord.  5,  New  posi- 
tion of  the  thyroid  cartilage.  6,  New  position  of  vocal  cords. 

The  true  vocal  cords  are  attached  to  the  anterior  angles,  or 
vocal  processes,  of  the  arytenoids;  the  crico-arytenoid  muscles  are 
inserted  into  the  external  angles. 

The  cartilages  of  Wrisberg  are  found  in  the  aryteno-epi^lottic 
folds. 

The  epiglottis  is  attached  to  the  inner  surface  of  the  anterior 
portion  of  the  thyroid  cartilage.  It  projects  upward  behind  the  base 
of  the  tongue.  The  epiglottis  is  attached  to  the  tongue  by  the  three 
glosso-epiglottic  folds. 

The  false  vocal  cords  are  two  folds  of  the  laryngeal  mucous  mem- 
brane which  pass  from  the  anterior  surfaces  of  the  arytenoids  to  the 
thyroid  cartilage.  Thev  are  located  above  the  true  vocal  cords. 


VOICE  AND  SPKK<  H. 


387 


The  true  vocal  cords  extend  from  the  anterior  angles  of  the  bases 
of  the  arytenoids  to  the  thyroid  cartilage. 

The  glottis  is  the  chink  between  the  true  vocal  cords. 

The  ventricle  of  the  larynx  is  the  pouch  between  the  true  and  false 

1  cords. 

THE  MUSCLES. — All  of  the  laryngeal  cartilages,  joined  together 
by  ligaments,  are  moved  by  five  pairs  of  muscles.  The  muscles  of  the 
larynx  are  divided  into  two  groups:  intrinsic  and  extrinsic.  To  the 
former  group  belong  those  muscles  which  are  attached  to  the  various 
cartilages.  The  latter  collection  comprises  the  musculature  connect- 
ing the  larynx  to  other  parts  like  the  hyoid  bone. 


r~\ 


Fig.  95.— Schematic  Horizontal  Section  of  Larynx.     (LAlfDOis.) 

7,  Position  of  horizontally  divided  arytenoid  cartilages  during  respiration. 
From  their  anterior  processes  run  the  converging  vocal  cords.  The  arrows 
show  the  line  of  traction  of  the  posterior  crico-arytenoid  muscles.  II,  II. 
Position  of  the  arytenoid  muscles  as  a  result  of  this  action. 

IXTIUNSICS. — Of  these  there  are  five  pairs. 

1.  The  Crico-thyroid  Muscles. — These,  which  are  in  the  anterior 
part  of  the  larynx,  originate  in  the  front  and  sides  of  the  cricoid  car- 
tilage below.     Outwardly  they  are  attached  on  each  side  to  the  lower 
edge  of  the  thyroid  cartilage.     They  become  fixed  by  the  action  of 
the  thyro-hyoid,  sterno-thyroid,  and  laryngo-pharyngeal  muscles. 

Action. — They  incline  the  cricoid  cartilage  upward  and  backward 
and  so  elongate  and  stretch  the  vocal  cords,  at  the  same  time  contract- 
ing the  opening  of  the  gl<v 

2.  The  Posterior  Crico-arytenoid  Muscles. — These  take  their  de- 
parture from  the  posterior  surface  of  the  shield  of  the  cricoid  cartilage. 


388 


PHYSIOLOGY. 


They  then  converge  and  are  fastened  to  the  base  of  the  corresponding 
arytenoid  cartilage. 

Action. — In  contracting  they  turn  the  anterior  ends  of  the  aryte- 
noids  outward,  whereby  they  separate  the  vocal  cords  from  each  other 
and  give  a  rhomboid  form  to  the  glottis.  Thus  it  is  materially 
widened. 

3.  The  Lateral  Crico-arytenoids. — These  muscles  are  found  upon 
the  inner  side  of  the  cricoid.  They  are  carried  backward  and  upward 
and  are  fastened  to  the  outside  of  the  posterior  ends  of  the  bases  of 
the  arytenoid  cartilages. 

Action. — In  contracting  they  rotate  the  arytenoid  cartilage  in- 
ward. They  are  antagonists  of  the  posterior  crico-arytenoid  muscles ; 
they  narrow  the  vocal  part  of  the  glottis. 


Fig.  96. — Schematic  Closure  of  the  Glottis  by  the  Thyro-arytenoid. 
Muscles.     (LANDOIS.) 

II,  II,  Position  of  the  arytenoid  cartilages  during  quiet  respiration.  The 
arrows  indicate  the  direction  of  muscular  traction.  /,  /,  Position  of  the 
arytenoid  cartilages  after  the  muscles  contract. 

4.  The  Thyro-arytenoid  Muscles. — This  pair  of  muscles  is  inserted 
at  the  anterior  end  in  the  middle  of  the  angle  of  the  thyroid  cartilage, 
and  at  the  posterior  end  is  fastened  to  the  inside  of  the  anterior  end 
of  the  base  of  the  arytenoid  cartilages.  Each  muscle  of  the  pair 
runs  its  entire  length  parallel  with  the  corresponding  vocal  cord. 

This  muscle  has  two  bundles :  an  internal  and  external  bundle. 
The  muscle  draws  the  arytenoids  toward  the  thyroid  and  relaxes  the 
cords.  By  the  internal  bundle  the  anterior  part  of  the  vocal  cord 
can  be  tightened  while  relaxing  the  posterior  part.  It  is  the  muscle 
concerned  in  the  production  of  the  high  notes  in  the  singing  voice. 


VOICE  AND  SPEECH.  389 

5.  The  Arytenoid  constitutes  an  odd  muscle.  It  extends  pos- 
teriorly between  the  two  arytenoid  cartilages.  The  muscle  is  divided 
into  two  layers:  one  posterior,  of  oblique  fibers  disposed  like  an  X; 
and  one  anterior,  of  transverse  fibers. 

Its  action  is,  in  contracting,  to  draw  the  arytenoid  cartilages 
together  so  that  the  respiratory  part  of  the  glottis  is  closed.  If  the 
contraction  be  simultaneous  with  that  of  the  lateral  crico-arytenoid 
muscles,  respiration  is  entirely  interrupted. 

THE  EXTRINSIC  MUSCLES  are  those  of  the  anterior  region  of  the 
neck :  those  in  the  suprahyoid  as  well  as  those  in  the  subhyoid  region. 
By  the  action  of  these  muscles  the  entire  larynx  is  moved  upward 
and  downward. 

THE  CAVITY  of  the  larynx  is  lined  with  a  mucous  membrane. 
The  mucous  membrane  is  continuous  with  that  of  the  trachea.  It  is 
covered  with  the  prismatic  or  ciliated  epithelium  in  all  places  ex- 
cept over  the  vocal  cords  and  epiglottis.  In  these  special  areas  it  is 
stratified. 

THE  VOCAL  CORDS  comprise  two  sets,  as  was  previously  men- 
tioned; the  upper,  false  cords,  composed  of  folds  of  mucous  mem- 
brane, take  no  part  in  voice  production;  the  lower,  true  cords,  are 
composed  of  a  mucous  membrane  with  pavement  epithelium,  a  lamina 
of  elastic  fibers,  and  the  thyro-arytenoid  muscle. 

Opening  the  cavity  of  the  pharynx  and  raising  the  epiglottis,  the 
whole  extent  of  the  glottis  is  seen;  that  is,  the  slit  left  by  the  two 
superior  cords.  This  has  the  shape  of  a  much  elongated  triangle — 
apex  in  front,  base  at  the  back.  The  limited  anterior  part  of  the 
triangle  is  called  the  vocal  part  of  the  glottis;  whereas  the  posterior 
part  is  called  the  respiratory  portion.  It  does  not  participate  in 
phonation,  but  only  in  the  passage  of  air. 

NERVE-SUPPLY. — The  nerves  which  are  distributed  to  the  larynx 
come  from  the  pneumogastric.  The  superior  laryngeal  nerve  supplies 
the  mucous  membrane  of  the  larynx  and  gives  the  external  laryngeal 
branch  to  the  crico-thyroid  muscle.  The  inferior,  or  recurrent,  laryn- 
geal nerve  supplies  all  of  the  muscles  except  the  crico-thyroid.  The 
ganglia  which  preside  over  the  motor  innervation  of  the  larynx  are 
seated  in  the  floor  of  the  fourth  ventricle. 

Laryngoscopy. — The  laryngoscope  is  an  instrument  that  is  used 
to  bring  to  the  user's  view  various  parts  of  the  pharynx,  larynx,  and 
trachea.  It  consists  of  a  small  mirror  fastened  to  a  long  handle. 
The  angle  that  the  mirror  makes  with  its  handle  is  from  125  to  130 
degrees. 


390  PHYSIOLOGY. 

CONDITION  OF  THE  VOCAL  COKDS. — By  observations  made  with  the 
laryngoscope  it  has  been  determined  that,  while  in  respiration  the 
vocal  cords  are  inclined  from  each  other,  and  the  glottis  is  wide  open, 
in  speaking  or  vocalization  the  cords  are  seen  to  approximate  and 
vibrate.  In  ordinary  quiet  breathing  there  is  a  wide,  triangular- 
shaped  opening  in  the  glottis.  On  the  other  hand,  during  the  produc- 
tion of  vocal  sounds  the  triangular  posterior  opening  is  completely 
closed,  while  the  anterior  portion  of  the  rima  glottidis  becomes  a  very 
fine  fissure,  or  slit.  • 

VOICE. 

It  is  the  vibration  of  the  edges  of  this  fissure  by  the  passage  of 
air  through  it  that  produces  sound :  the  voice.  The  air  expelled  from 
the  lungs  acquires  a  maximum  of  tension  in  the  narrow  tracheal 


Fig.  97. — Position  of  Vocal  Cords  on  Uttering  a  High  Note.     (L-ANDOis.) 

tube,  causing  it  to  strike  underneath  the  true  vocal  cords  and  put 
them  into  the  proper  vibrations.  But  the  tone  produced  will  not 
always  be  of  the  same  caliber  and  height,  since  the  expired  air  may 
find  the  vocal  cords  in  different  states,  the  result  of  muscular  con- 
tractions. 

The  Height  of  the  sound  produced  in  the  larynx  depends  upon 
the  number  of  vibrations  of  the  vocal  cords  during  a  given  time.  The 
number  of  vibrations  would  then  depend  upon  the  state  of  tension 
and  the  length  of  the  cords  themselves.  The  greater  the  number 
of  vibrations  during  a  second,  the  higher  will  be  the  tone,  and  vice 
versa. 

The  range  of  the  human  voice,  as  regards  height,  is  usually  be- 
tween 87  and  768  vibrations  per  second.  Not  all  persons  have  such  a 
range.  Each  type  of  voice  includes  about  two  octaves.  When  a  man 
speaks — that  is,  when  he  uses  the  articulate  voice — his  voice  does  not 
exceed  a  height  of  a  half-octave.  When  he  sings  his  vocal  range  is 
more  extended. 


VOICE  AND  SPEECH.  391 

The  Intensity  of  sound  depends  upon  the  extent  of  the  vibrations 
of  the  vocal  cords,  produced  especially  by  the  force  of  the  current  of  air. 

The  height  of  the  voice  depends,  to  a  considerable  extent,  upon 
different  lengths  of  the  vocal  cords.  The  result  is  that  in  adult  man 
the  boss,  'baritone, }  and  tenor  voices  are  found,  because  of  the  greater 
length  of  the  vocal  cords  in  man.  On  the  contrary,  the  contralto, 
mezzosoprano,  and  soprano  voices  belong  to  women  and  boys,  for  they 
have  cords  shorter  in  length. 

Timbre  of  sound  depends  upon  the  nature  of  the  vibrating  body 
and  of  the  other  means  vibrating  at  the  same  time  with  it  for  the 
production  of  harmonious  sounds. 

Resonance. — The  normal  voice  of  man  is  sonorous;  that  is,  it 
is  composed  of  vibrations  regular  in  extent  and  isochronous.  Its 
resonance  comes  either  from  the  air-tube  or  from  the  resonators.  By 
the  former  is  understood  the  trachea,  bronchi,  walls  of  the  lungs,  and 
thoracic  case ;  by  the  latter,  the  ventricles,  pharynx,  mouth,  and  nasal 
cavities.  The  resonance  within  the  thorax  in  an  adult  causes  a 
fremitus  of  the  thoracic  wall.  This  is  greatly  increased  in  low  sounds 
and  diminishes  until  it  disappears  in  high  sounds. 

Ordinarily,  in  speaking  and  singing,  the  air  put  in  vibration  in 
the  larynx  issues  from  the  mouth  while  the  nostrils  are  open.  If  they 
be  closed,  the  air  which  is  held  there  vibrates  with  the  air  issuing 
through  the  oral  cavity  and  gives  the  voice  a  nasal  tone. 

The  human  voice  can  assume  two  different  registers.  The  one  is 
strong  and  sonorous  and  accompanied  with  vibrations  of  the  thoracic 
wall  (chest-voice).  The  other  is  weak,  without  resonance,  and  of 
higher  pitch  (head-voice,  or  falsetto). 

Ventriloquy,  which  by  practice  can  reach  great  perfection,  con- 
sists only  in  the  possibility  of  changing  the  register  of  the  voice.  The 
name  derived  its  origin  from  the  erroneous  interpretation  of  it  by  the 
ancients.  They  claimed  that  the  ventriloquists  spoke  from  the  stom- 
ach. The  performer  is  able  to  conduct  dialogues  in  which  two  persons 
appear  to  take  part. 

Speech. — If  man  had  the  faculty  of  making  only  sounds  with  the 
larynx,  his  vocal  organ  would  not  differ  greatly  from  ordinary  musical 
instruments.  The  voice  in  such  case  would  but  serve  to  make  others 
aware  of  his  presence  and  to  call  them  for  the  various  wants  of  life,  as 
happens  in  animals  and  in  the  child  itself  when  just  born. 

But  man  is  endowed  with  an  important  means  by  which  he  can 
communicate  to  his  fellows  the  state  of  his  mind.  It  forms  one  of 
man's  noblest  characteristics,  a  distinctive  one. 


392  PHYSIOLOGY. 

The  infant  at  first  expresses  the  state  of  his  mind  by  cries  accom- 
panied by  gestures.  Then  little  by  little  it  learns  and  tries  to  imitate 
those  sounds  which  the  parents  always  make  corresponding  to  given 
objects  and  persons.  It  pronounces  them  without  understanding  their 
meaning.  In  later  years  it  learns  of  the  correspondence  of  given 
sounds  to  given  objects  and  ideas. 

Speech  is  articulate  voice.  It  is  an  ensemble  of  sounds  and  noises 
harmonized  by  the  will  and  co-ordinated  by  a  particular  cortico-motor 
nervous  center.  Its  aim  is  the  making  known  to  the  listener  the  pres- 
ent state  of  mind  of  the  speaker  as  well  as  recollections  of  the  past  and 
tendencies  toward  the  future. 

VOWELS  AND  CONSONANTS. — Speech  is  composed  of  two  elements, 
namely:  vowels  and  consonants.  The  former  consist  of  sounds  gen- 
erated in  the  larynx  and  slightly  modified  in  the  pharynx  and  mouth- 
cavity.  The  consonants  result  from  noises  variously  produced  by  the 
obstacles  encountered  by  the  air  in  its  passage  through  the  pharynx 
and  mouth-cavity.  Vowels  are  produced  in  the  larynx,  pharynx,  and 
mouth;  consonants  not  in  the  larynx,  but  in  the  mouth. 

The  vowels  are  produced  by  the  different  form  of  the  cavity  of 
the  pharynx  and  mouth  during  the  expiration  of  air  through  them. 
The  principal  change  in  form  consists  in  the  lengthening  and  shorten- 
ing of  the  mouth.  The  vowels  are  a,  e,  i,  o,  and  u. 

The  consonants  consist  of  sounds  emitted  by  the  larynx,  but  which 
become  noises  by  reason  of  obstacles  they  encounter.  According  to 
the  obstructions  met  with,  consonants  are  termed  gutturals  (h,  fc,  q), 
linguals  (c,  d,  g,  t,  s,  n,  I,  r),  and  labials  (b,  f,  m,  p,  v).  The  linguals 
are  subdivided  into  palatals  and  dentals. 

The  very  varied  union  of  the  vowels  with  the  consonants  consti- 
tutes syllables;  union  of  the  latter  forms  words. 

Stammering  is  due  to  a  continued  spasmodic  contraction  of  the 
diaphragm  and  to  the  muscles  of  the  larynx  not  harmonizing  the  chink 
of  the  glottis. 

Stuttering  is  due  to  a  want  of  ability  to  form  the  proper  sounds 
by  the  laryngeal  muscles;  the  breathing  and  diaphragm  are  both 
normal. 

Pathology. — Paralysis  of  the  motor  nerves  of  the  larynx  from 
the  pressure  of  tumors,  causes  aphonia,  or  loss  of  voice.  In  aneurism 
of  the  aortic  arch  the  left  recurrent  nerve  may  be  paralyzed  from 
pressure.  The  laryngeal  nerves  may  be  temporarily  paralyzed  by 
overexertion  and  hysteria. 


VOICE  AND  SPEECH.  393 

If  one  vocal  cord  be  paralyzed,  the  voice  is  impure  in  tone  and 
falsettolike. 

Hoarseness  may  be  caused  by  mucus  upon  the  vocal  cords  or  by 
roughness  or  laxness  of  the  cords.  Disease  of  the  pharynx  or  naso- 
pharynx and  uvula  may,  in  a  reflex  manner,  produce  a  change  in  the 
voice. 


CHAPTER  XIII. 

ELECTRO=PHYSIOLOGY. 

To  IRRITATE  nerves  we  employ  the  du  Bois-Reymond  induction 
apparatus.  It  consists  of  a  primary  spiral  of  some  130  coils  of  wire 
and  a  secondary  spiral  of  6000  coils  of  wire.  The  core  inside  the 
primary  spiral  is  formed  of  a  number  of  thin  iron  wires.  To  graduate 
the  current  the  secondary  spiral  is  moved  in  a  groove  to  and  from 
the  primary,  or,  following  Bowditch,  it  can  be  rotated  at  an  angle 
to  the  primary  spiral.  A  wooden  scale  at  the  side  shows  the  separa- 
tion of  the  coils  in  millimeters.  The  strength  of  the  current  at  the 
different  separations  of  the  coils  can  also  be  graduated  by  means  of  the 
galvanometer.  To  break  the  current  Neef's  automatic  hammer  is 
used.  The  break  shock  is  stronger  than  the  make  shock.  To  equalize 
the  shocks,  Helmholtz  used  a  side  wire  to  make  an  accessory  current. 

To  study  the  currents  of  muscles  or  nerves  it  is  necessary  to  use 
various  kinds  of  apparatus  devised  by  du  Bois-Eeymond.  To  use  the 
galvanometer  (instead  of  the  usual  wire  electrodes)  we  make  use  of 
nonpolarizable  electrodes.  They  are  formed  of  flat,  glass  tubes  and 
their  lower  end  is  closed  water-tight  by  means  of  common  salt  clay 
(kaolin),  which  externally  is  molded  into  a  hooklike  shape  for  the 
nerve  to  rest  on.  A  strip  of  amalgamated  zinc  plate  is  inserted  into 
the  glass  tube  filled  with  a  concentrated  solution  of  sulphate  of  zinc. 
The  zinc  is  fastened  to  a  piece  of  brass  which  has  a  screw  for  the 
attachment  of  the  wire  to  lead  off  the  current  to  the  galvanometer. 
Instead  of  the  galvanometer  the  capillary  electrometer  may  be  used. 

The  current  of  the  muscle  or  nerve  traverses  the  muscle  or  nerve 
and  produces  a  deflection  of  the  needle  of  the  galvanometer,  which 
indicates  the  direction  of  the  current. 

Physiological  Rheoscope. — This  name  has  been  given  to  the  nerve- 
muscle  preparation  of  the  frog  where  the  greatest  possible  length  of 
the  sciatic  nerve  attached  may  be  used.  The  preparation  of  the  nerve 
requires  special  care,  for  the  nerve  must  be  removed  by  a  little  seeker 
of  glass  or  bone.  No  metal  must  touch  it.  It  is  removed  from  below 
(394) 


ELECTRO-PHYSIOLOGY.  395 

upward,  and  if  properly  done  there  should  be  no  contraction  of  the 
muscle  during  the  operation.  If  the  nerve  of  this  preparation  be 
brought  into  contact  with  a  segment  of  separated  muscle  so  as  to  touch 
simultaneously  the  longitudinal  and  transverse  surfaces,  a  contraction 
instantly  follows.  If  a  piece  of  the  muscle  be  placed  on  the  electrodes 
of  du  Bois-Reymond  so  that  the  transverse  section  corresponds  to  one 
and  the  longitudinal  surface  to  the  other,  the  deflection  of  the  needle 
of  the  galvanometer  indicates  the  existence  of  a  current  in  the  muscle 
which  passes  from  the  transverse  to  the  longitudinal  surface.  The 
surface  of  the  muscle  is  positive  and  that  of  the  transversely  divided 
segment  negative.  Instead  of  a  transverse  section  of  a  muscle  its 
tendon  may  be  taken,  which  is  also  negative  and  has  been  called  the 


Fig.  98. — The  Nerve-muscle  Preparation.     (STIRLING.) 
S,  The  Nerve-muscle.     /<',  Lower  third  of  femur.      /,  Tendon  of  gastrocnemius  muscle. 

natural  transverse  surface.  The  cut  surface  of  a  longitudinal  section 
of  muscle  presents  positive  electrization.  The  laws  of  electrical  cur- 
rents of  muscle  have  been  fully  determined  by  du  Bois-Reymond: — 

1.  When  the  conductor  unites  the  longitudinal  to  the  transverse 
surface  there  is  a  well-marked  deviation  of  the  needle,  and  the  greatest 
deviation  occurs  when  the  middle  of  the  longitudinal  surface  is  con- 
nected with  the  middle  of  the  transverse. 

2.  When  two  points  are  connected  on  a  longitudinal  or  transverse 
surface  which  are  unequally  distant  from  the  middle,  or  two  points 
unequally  distant  on  opposed  surfaces,  then  there  is  a  slight  deflection 
of  the  needle.     In  the  case  of  the  longitudinal  surfaces  the  current 
passes  along  the  conductor  from  the  point  nearer  the  center  to  the  one 
farther  off.     The  reverse  is  the  case  for  the  transverse. 


396  PHYSIOLOGY. 

3.  When  two  points  are  connected  on  the  same  or  on  opposed 
surfaces  equally  distant  from  the  center,  or  when  the  centers  of  two 
opposite  surfaces  are  joined,  there  is  no  movement  of  the  needle  of 
the  galvanometer. 

The  parelectronomic  part  of  the  muscle  is  the  tendinous  part  of 
the  muscle,  which  is  negative  instead  of  being  positive,  as  is  the  rule. 
Here  it  is  necessary  to  make  an  artificial  section  for  the  purpose  of 
demonstrating  the  electrical  phenomena  of  muscle. 

Hermann  has  shown  that  the  muscle-currents  are  the  result  of 
the  preparation,  and  do  not  exist  in  the  normal,  intact  fibers  when  in 
a  state  of  repose.  These  galvanometrical  deviations  are  due  to  the 
traumatic  action  of  air,  cold,  or  chemicals. 

Electrical  Phenomena  of  Contracting  Muscle. — If  upon  the  elec- 
trodes connecting  the  poles  of  the  galvanometer  a  muscle  is  so  placed 
that  the  needle  deflects,  and  then  tetanize  the  muscle  by  stimulating 
its  nerve,  the  needle  will  be  seen  to  retrace  its  movement  of  deflection. 
This  reverse  of  the  natural  current  is  known  as  negative  deviation. 
This  has  been  shown  to  be  due  to  a  weakening  of  the  natural  nerve- 
current,  and  not  to  the  production  of  a  new  one  contrary  to  the  current 
of  rest.  This  negative  variation  can  stimulate  the  nerve  of  another 
muscle  if  the  nerve  of  the  physiological  rheoscope  be  placed  on  the 
nerve  of  a  contracting  muscle  in  such  a  manner  that  the  first  touches 
both  the  cut  surface  and  another  point  on  the  second  nerve ;  then  each 
contraction  of  the  muscle  is  followed  by  a  contraction  of  frog's  nerve- 
muscle  preparation  (secondary  contraction).  This  negative  variation 
lasts  about  0.004  second  and  is  propagated  along  the  muscle  with  the 
same  velocity  as  the  wave  of  contraction  it  precedes,  vanishing  even 
before  the  arrival  of  the  latter.  Hermann  calls  the  negative  variation 
by  the  name  of  current  activity. 

Negative  Variation  of  the  Nerve-current. — If  you  place  upon  the 
electrodes  connected  with  the  galvanometer  a  piece  of  nerve,  the  devia- 
tion of  the  needle  shows  the  existence  of  the  nerve-current  already 
described  so  long  as  the  nerve  is  at  rest.  If  you  tetanize  the  nerve 
the  needle  is  seen  to  run  back  toward  zero,  and  sometimes  even  beyond 
it.  This  takes  place  in  every  kind  of  nerve  and  in  the  whole  length 
of  the  nerve.  It  can  be  produced  by  mechanical  or  chemical  stimuli  as 
readily  as  with  electricity.  The  greater  the  stimulus,  the  greater  the 
negative  variation,  but  there  is  not  a  definite  proportion  between 
them.  Hermann  has  shown  that  neither  in  the  nerve  nor  muscle  do 
any  of  these  currents  exist  so  long  as  the  structures  are  uninjured.  To 
generate  a  nerve-current  in  repose  it  is  necessary  to  make  a  transverse 


ELECTRO-PHYSIOLOGY.  397 

section.  This  produces  death  of  the  superficial  layer  of  a  segment 
next  the  cut  surface.  The  dead  tissue  behaves  negatively  with  regard 
to  the  living,  and  the  electromotor  forces  accordingly  have  their  seat 
at  the  plane  of  demarcation  between  the  dead  and  living.  As  to  the 
currents  of  activity.,  they  are  explained  by  admitting  that  during 
stimulation  the  active  parts  are  negative  with  regard  to  the  parts  at 
rest. 


CHAPTER   XIV. 

THE   ANATOMY   AND   PHYSIOLOGY   OF   THE 
NERVOUS   SYSTEM. 

ANATOMY  OF  THE  NERVOUS  SYSTEM   (EXCEPT  THE 
CEREBELLUM).1 

STRUCTURE  OF  NERVE=TISSUE. 

NERVE-TISSUES  present  themselves  in  two  varieties :  some  as  white 
substance  and  some  as  gray  substance.  These  two  substances  are  dif- 
ferent, not  only  in  color,  but  also  in  physical  and  chemical  properties 
and  in  anatomical  arrangement. 

The  gray  substance  contains  as  characteristic  elements  the  nerve- 
cells;  the  white  substance,  the  nerve- fibers.  These  latter  emerge  from 
the  gray  nervous  substance  to  branch  out  toward  the  peripheral  organs. 
These  two  substances,  gray  and  white,  possess  a  common  element 
known  as  neuroglia;  in  addition,  each  contains  blood-vessels. 

The  Nerve-cell. — The  nerve-cell  is  the  characteristic  funda- 
mental element  of  the  gray  substance:  it  is  the  unit  of  the  nervous 
system.  It  is  the  element  which  gives  to  this  kind  of  nervous  tissue 
its  gray  color.  When  these  units  are  charged  with  a  strong  portion  of 
pigment,  they  are  black,  as  in  the  locus  niger  of  the  cerebral  peduncles. 
When  a  little  less  pigmented  they  present  a  grayish  color:  the  color 
that  is  characteristic  of  the  brain  and  the  central  portion  of  the  spinal 
cord.  They  may  be  charged  with  red  pigment,  then  the  cells  are 
reddish;  such  cells  constitute  the  red  nucleus  of  the  head  of  the 
cerebral  crura. 

STRUCTURE  OF  THE  NERVE-CELL. — The  nerve-cell  is  composed 
of  ( 1 )  a  mass  of  protoplasm  inclosing  ,a  nucleus  with  its  nucleolus ; 
(2)  of  simple  or  branched  prolongations.  The  protoplasm  of  a  nerve- 
cell,  like  that  of  many  other  cells,  is  formed  of  a  very  delicate  network 
of  bands  whose  meshes  are  filled  with  a  clear  or  finely  granular 
albuminoid  substance.  The  network  has  been  designated  by  the  name 
of  spongioplasm  and  the  intermediate  substance  is  generally  termed 


1  For  anatomy  of  the  cerebellum  see  subsequent  pages. 
(398) 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


399 


Fig.  99.— The  Structure  of  Nervous  Tissue.     (LANDOis.) 

1,  Primitive  fibril.  2,  Axis-cylinder.  3,  Remak's  fiber.  4,  Medullated 
varicose  fiber.  5,  6,  Medullated  fiber  with  Schwann's  sheath.  G,  Neuri- 
lemma.  t,  t,  Ranvier's  nodes.  6,  White  substance  of  Schwann.  d,  Cells  of 
the  endoneurium.  a,  Axis-cylinder,  x,  Myelin  drops.  7,  Transverse  section  of 
nerve-fiber.  8,  Nerve-fiber  acted  on  with  silver  nitrate.  7,  Multipolar  nerve- 
cell  from  spinal  cord,  z,  Axial  cylinder  process,  y,  Protoplasmic  processes; 
to  the  right  of  it  a  bipolar  cell.  II,  Peripheral  ganglionic  cell  with  a  con- 
nective-tissue capsule.  ///,  Ganglionic  cell,  with  o,  a  spiral,  and  n,  straight 
process,  m,  Sheath. 


400  PHYSIOLOGY. 

hyaloplasm.  As  to  these  two  components,  the  protoplasm  of  nerve- 
cells  is  like  that  of  most  other  cells. 

Fibrils. — One  peculiarity  is  the  presence  in  it  of  fibrils  which 
run  through  its  substance. 

Granules. — The  other  characteristic  feature  of  nerve-protoplasm 
is  the  existence  within  it  of  angular  granules.  These  show  a  special 
liking  for  basic  aniline  dyes,  as  methylene  blue.  By  many  authors 
they  are  spoken  of  as  Nissl  bodies,  after  their  discoverer  and  the  man 
who  has  demonstrated  their  physiological  worth.  The  granules  are 
found  scattered  throughout  the  cell-body  and  its  dendrons,  but  not 
in  the  axis-cylinder  and  the  adjacent  area  of  the  cell  to  which  it  is 
attached. 

The  most  important  relations  that  these  granules  bear  physio- 
logically to  the  cell  is  as  follows:  Under  either  normal  or  abnormal 
activity  of  the  nerve-cell  the  granules  undergo  a  change  which  has 
been  termed  chromatolysis.  It  is  a  slow  dissolution  of  the  granules 
with  diffusion  of  the  degenerated  product  into  the  protoplasm.  At 
first  the  cell  swells,  pushing  its  nucleus  to  one  side;  later  the  cell 
diminishes  in  size,  due  to  loss  of  its  chromatophilic  substance. 

It  is  in  the  hyaloplasm  that  the  pigment  substance  which  gives 
to  the  cell  its  particular  color  is  deposited. 

Nucleus. — The  nucleus  of  the  nerve-cell  forms  a  small,  rounded 
or  oval  mass.  It  is  characterized  by  its  relatively  large  size.  This 
nucleus  is  strongly  colored  by  all  the  reagents,  as  carmine,  methylene 
blue,  etc.  Around  the  nucleus  the  chromatin  forms  a  sort  of  cell-wall 
called  the  nuclear  membrane.  Within  the  nucleus  is  seen  a  small 
refracting  body  called  the  nucleolus.  Its  chromatin  is  relatively  great 
in  amount. 

Cell-prolongations. — From  the  researches  of  Deiters  it  has  been 
learned  that  nearly  every  nerve-cell  has  protruding  from  its  periphery 
a  greater  or  less  number  of  prolongations.  These  are  of  two  varieties : 
one  is  unique,  nonbranching,  and  prolonged  under  the  form  of  a 
cylinder-axis  of  a  nerve.  It  is  known  by  the  various  terms,  axis- 
cylinder,  neuraxon,  and  neurite.  The  other  variety  of  prolongations 
is  composed  of  many,  though  an  uncertain  number  of,  processes.  This 
new  set  of  prolongations  bears  the  name  of  protoplasmic  processes, 
dendrons,  dendrites,  or  the  poles  of  the  cells.  Some  cells  possess  no 
•dendrons,  others  very  many.  However,  it  is  believed  that  no  cell  is 
without  its  neuraxon.  According  to  Cajal,  the  communications  of  the 
prolongations  of  the  cells  among  themselves  is  no  more  than  that  of 
simple  contact.  It  is  analogous  to  the  contact  which  permits  of  the 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          4Q1 

passage  of  the  electrical  current  when  the  two  electrodes  of  an  electrical 
battery  are  in  contact.  Further,  the  nervous  impulses  are  transmitted 
only  along  the  neuraxons  from  cell  to  cell.  Each  neuraxon,  by  branch- 
ing and  coming  in  contact  with  the  dendrons  of  other  and  neighboring 
cells,  conveys  its  impulse  to  them.  They  in  turn  transmit  it  cen- 
tripetally  to  the  axis-cylinders  of  their  own  cells,  to  be  further  trans- 
mitted to  other  cells.  According  to  this  doctrine  the  nerve-cell 
would  be  physiologically  unipolar.  To  denote  this  close  contact  exist- 
ing between  the  axis-cylinder  and  dendrons  of  various  cells,  Foster 
has  used  the  term  "syn  apsis." 

The  nerve-cells  of  the  gray  matter  are  of  various  sizes  and  shapes, 
the  branched,  stellate,  or  multipolar  form  being  predominant.  Some 
are  more  or  less  bipolar  or  spindle-shaped ;  however,  at  each  extremity 
there  is  usually  a  fine  plexus  of  branches.  Some  are  ovoid  or  pyri- 
form,  as  in  the  cortex  of  the  cerebellum,  where  they  have  received 
the  name  of  cells  of  Purkinje.  The  cells  of  the  ganglia  of  the  spinal 
nerves  are,  in  great  part,  unipolar. 

The  dimensions  of  the  nerve-cells  are  very  variable ;  the  smallest 
are  about  1/400o  incn  in  diameter,  the  cells  of  the  posterior  horns  of 
the  spinal  cord  are  from  1/250o  to  Yi2oo  inch,  and  the  giant  cells  of  the 
anterior  horns  of  the  spinal  cord  are  about  1/250  inch  in  diameter. 

By  employing  Golgr's  silver-nitrate  method  of  staining,  the 
nerve-cells,  with  their  processes,  are  stained  black  from  a  deposition 
of  the  silver.  By  reason  of  this,  the  nerve-prolongations  may  be 
traced  to  their  ultimate  terminations.  This  method  beautifully  dem- 
onstrates the  distribution  of  the  dendrites,  their  branching,  and  man- 
ner of  contact  with  dendrites  of  contiguous  cells ;  also,  how,  as  a  rule, 
the  neuraxon  does  no  very  immediate  branching.  It  must  be  stated, 
though,  that  there  usually  proceed  from  the  neuraxon  numerous  fine 
fibrils  to  which  the  term  collaterals  is  applied.  These  are  in  com- 
munication with  the  dendrites  of  neighboring  cells.  The  neuraxon 
in  nerve-centers  after  proceeding  for  some  distance  does  really  branch 
to  form  arborizations  to  come  into  contact  with  nerve-dendrites. 

THE  NERVE-FIBERS. — Every  nerve-fiber  is  a  process  of  a  nerve- 
cell.  It  is  the  neuraxon  of  some  particular  cell.  It  is  the  medium 
which  conducts  impulses  to  or  from  the  tissues  and  organs,  on  the 
one  hand,  and  the  nerve-centers,  on  the  other.  In  the  majority  of 
cells  the  neuraxon  acquires  a  sheath  to  be  thus  converted  into  a  medul- 
lated  nerve-fiber.  Thus,  there  are  two  kinds  of  nerve-fibers :  medul- 
lated,  or  those  with  myelin;  and  nonmedullated,  or  those  without 
myelin. 


26 


402  PHYSIOLOGY. 

Nedullatecl  Fibers  in  the  fresh  condition  are  bright,  glistening- 
cylinders  showing  a  dark,  double  contour.  The  essential  part  of  it  is 
the  axis-cylinder.  This  is  a  soft,  transparent  rod,  or  thread,  which 
runs  from  one  end  of  the  fiber  to  the  other.  It  does  not  anastomose 
with  its  neighbors,  and  in  the  average  nerve  is  about  1/120o  incn  in 
diameter.  After  the  employment  of  certain  reagents  the  axis-cylinder 
shows  itself  to  be  composed  of  very  fine,  homogeneous  or  more  or  less 
beaded  fibrillaa.  The  latter  are  the  elementary,  or  primitive,  fibrillce. 
They  are  held  together  by  a  small  amount  of  a  faintly  granular,  inter- 
stitial substance.  The  thickness  of  the  axis-cylinder  is  in  direct  pro- 
portion to  the  thickness  of  the  whole  nerve-fiber.  The  axis-cylinder 
is  enveloped  in  its  own,  more  or  less  elastic,  hyaline  sheath. 

The  axis-cylinder  is  not  regularly  cylindrical,  but  is  slightly 
narrowed  in  places.  Under  the  influence  of  silver  nitrate  applied 
to  its  surface  there  appear  alternate  obscure  and  clear  transverse  striae. 
They  are  the  so-called  lines  of  Frommann. 

Nyelin. — Surrounding  the  axis-cylinder  is  the  myelin,  medullary 
sheath,  or  the  white  substance  of  Schwann.  It  is  a  layer  of  fatty 
substance,  strongly  refracting,  and  of  homogeneous  aspect.  It  is 
colored  black  by  osmic  acid.  It  is  the  myelin  which  gives  to  the 
nerve  its  double  contour.  It  is  composed  of  a  network  of  fibrils  of 
a  chemical  substance  called  neurokeratin;  which  incloses  the  semi- 
fluid, fatty  substance.  The  latter  contains,  among  other  substances,  a 
complex,  phosphorized  fat. 

The  sheath  of  myelin  envelops  the  axis-cylinder  everywhere,  ex- 
cept at  its  termination  and  at  the  nodes  of  Eanvier. 

In  its  arrangement  the  myelin  is  imbricated  in  the  fashion  of  tiles 
on  a  roof  by  reason  of  a  series  of  segments  one  above  the  other.  They 
are  separated  one  from  the  other  by  clear  lines.  The  lines  are  known 
as  the  incisures  of  Lantermann,  and  the  segments  as  those  of  Schmidt. 

Neurilemma. — The  neurilemma,  or  sheath  of  Schwann,  surrounds 
the  medullary  sheath  to  form  the  outer  boundary  of  the  nerve-fiber. 
It  is  a  thin,  elastic,  very  delicate,  hyaline,  and  transparent  membrane. 
It  is  comparable  to  the  cell-wall  of  a  cell.  Between  the  neurilemma 
and  medullary  sheath  there  are  irregularly  scattered  ovoid  nuclei. 
They  are  the  nerve-corpuscles,  and  are  analogous  to  the  muscle- 
corpuscles  previously  mentioned.  Each  nerve-corpuscle  is  surrounded 
by  a  thin  zone  of  protoplasm. 

Between  the  myelin  layer  and  the  neurilemma  is  a  thin  zone  of 
protoplasm.  When  this  arrives  at  the  level  of  the  annular  constric- 
tions it  is  reflected  upon  itself  to  line  the  internal  surface  of  the 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          493 

myelin  layer.  The  protoplasm  is  also  insinuated  into  the  incisures 
of  Lantermann  and  decomposes  the  layer  of  myelin  into  the  superposed 
segments  of  Schmidt. 

Socles  of  Ranvier. — At  intervals  of  about  one  millimeter  along 
the  course  of  the  nerve  there  appear  constrictions:  the  nodes  of 
Eanvier.  At  these  points  the  myelin  sheath  is  interrupted  so  that 
the  neurilemma  appears  to  do  the  constricting.  That  portion  of  the 
nerve-fiber  between  any  two  constrictions  is  termed  an  internodal  seg- 
ment. At  about  the  center  of  each  internodal  segment  is  located  one, 
sometimes  more,  nerve-corpuscles. 

Such  is  the  composition  of  a  medullated  nerve-fiber.  This  type 
of  nerve  is  found  chiefly  in  the  white  matter  of  the  nerve-centers  and 
in  the  cerebro-spinal  nerves,  with  the  exception  of  the  olfactory  nerve. 

XOXMEDULLATED  NERVE-FIBERS. — They  occur  especially  in  the 
sympathetic  s}Tstem,  but  are  also  present  in  the  cerebro-spinal  nerves 
to  a  slight  extent. 

Each  fiber  consists  of  a  bundle  of  fibrils — primitive  fibrils — 
which  are  inclosed  in  a  delicate,  transparent,  and  elastic  sheath.  The 
fibrils  are  very  delicate  and  somewhat  flattened.  Here  and  there  along 
the  course  of  the  fibrils  will  be  found  oval  nuclei.  These  latter  lie 
between  the  axis-cylinders  and  their  enveloping  neurilemma.  As  these 
fibrils  contain  no  myelin,  they  are  not  blackened  by  osmic  acid.  This 
allows  of  a  differentiation  between  medullated  and  nonmedullated 
nerves  when  examining  the  nerve-supply  of  a  tissue. 

NERVE-TRUNKS  consist  of  bundles  of  nerve-fibers.  Each  bundle, 
of  course,  contains  a  greater  or  less  number  of  fibrils.  Several  bundles 
are  held  together  by  a  common  connective-tissue  sheath:  the  epi- 
neurium.  Delicate  fibrils  lie  between  the  nerve-fibers  to  constitute 
the  endoneurium.  The  larger  blood-  and  lymph-  vessels  lie  in  the 
epineurium;  the  few  capillaries  of  the  nerve-fibers  lie  supported  in 
the  endoneurium. 

Termination  of  the  Nerve. — After  a  certain  course  in  the  trunk 
of  the  nerve  the  nerve-fiber  divides  at  the  periphery  into  a  terminal 
plaque,  the  motor  plaque  of  muscles;  or  into  a  sense-cell,  as  in  the 
retinal  cells  or  organ  of  Corti;  or  into  a  sense-corpuscle,  as  a  tactile 
corpuscle;  or  into  numerous  fibrils  which  anastomose  to  form  a 
terminal  plexus,  as  in  the  cornea. 

NOXMEDULLATED  FIBERS — that  is,  those  that  are  naked,  pale  or 
gray,  and  reduced  to  an  axis-cylinder  and  sheath — branch  and  form 
networks:  their  peripheral  terminations.  This  mode  of  termination 
occurs  in  the  nerve-fibers  of  common  sensation,  as  in  many  of  the 


404  PHYSIOLOGY. 

nerve-fibers  of  the  skin,  cornea,  and  mucous  membrane.  In  all  of 
these  cases  the  peripheral  termination  fibrils  are  intra-epithelial : 
that  is,  they  are  situated  in  the  epithelial  portions  of  cornea,  mucous 
membrane,  etc. 

Neuroglia. — In  the  gray,  as  well  as  in  the  white,  substance  of 
the  nerve-centers  there  exists  between  the  cells  and  nerve-fibers  an 
intervening  substance  which  has  been  termed  neuroglia.  It  must  not 
be  confounded  with  the  true  connective-tissue  along  the  course  of 
the  blood-vessels  in  the  nerve-centers.  Its  chemical  nature  is  wholly 
different  from  the  latter,  which  is  always  derived  from  the  mesoblast. 
Eanvier  has  shown  that  neuroglia  is  derived  from  the  primitive  neuro- 
blast  or  epiblast. 

Neuroglia  sometimes  presents  itself  in  the  shape  of  very  fine  fila- 
ments assembled  in  a  very  close  network,  as  in  the  gray  substance. 
Sometimes,  again,  it  is  seen  under  the  aspect  of  reticulated  plates 
bounding  the  space  in  which  the  nerve-fibers  pass.  This  is  beautifully 
demonstrated  in  the  white  substance  of  the  columns  of  the  spinal  cord. 

Elsewhere  the  neuroglia  is  found  to  be  a  homogeneous,  gelatini- 
f  orm  substance,  as  in  the  ependyma  of  the  spinal  cord  or  in  the  gelat- 
inous substance  of  Eolando  in  the  postero-lateral  groove  of  the  same 
structure. 

Besides  the  fibers  and  plates  already  mentioned,  neuroglia  con- 
tains cells.  These  are  star-shaped,  flat,  and  nucleated.  They  have 
numerous  prolongations.  By  the  aid  of  these  prolongations  the  cells 
of  the  neuroglia  are  freely  in  contact  with  one  another  to  form  a  very 
complicated  network.  This  incloses  in  its  meshes  the  nerve-elements. 

Neuroglia  enjoys  the  role  of  a  true  cement  which  unites  all  of 
the  fibers  and  nerve-cells. 

Classification  of  Nerve-cells. — According  to  Schafer,  nerve-cells 
are  broadly  classified  into :  "1.  Afferent  cells,  which  receive  impressions 
at  the  periphery  to  convert  them  into  impulses.  The  latter  then  pass 
toward  the  central  nervous  system.  2.  Efferent  cells,  which  send 
out  nervous  impressions  toward  the  periphery.  3.  Intermediary  cells, 
which  receive  impressions  from  afferent  cells  to  transmit  them  directly 
or  indirectly  to  efferent  cells.  4.  Distributing  cells,  which  occur  near 
the  periphery,  and,  receiving  impulses  from  efferent  cells,  distribute 
them  to  involuntary  muscles  and  secreting  cells.  The  cells  of  this 
class  belong  to  the  so-called  sympathetic  system. 

"The  afferent  and  efferent  cells  are  known  as  root-cells.  The 
greater  number  of  the  nerve-cells  of  the  brain  and  cord  belong  to  the 
intermediate  class.  They  serve  the  purposes  of  association  and  co- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          405 

ordination  and  afford  a  physical  basis  for  psychical  phenomena." 
Efferent  fibers  are  also  called  cellulifugal.  Afferent  fibers  are  also 
called  cellulipetal. 

Structure  of  the  Gray  Substance. — The  gray  matter  is  formed 
(1)  of  nerve-cells,  (2)  of  neuroglia-cells,  (3)  of  fibril  elements  repre- 
senting the  prolongations  of  nerve-  and  neuroglia-  cells,  (4)  of  an 
intervening  network  formed  by  the  branching  fibrils,  and  (5)  of 
blood-vessels.  Elements  1,  2,  and  3  (here  enumerated)  of  the  struc- 
ture have  been  treated  previously  in  detail. 

The  blood-vessels  penetrate  the  gray  substance,  and  are  sur- 
rounded with  a  layer  of  connective  tissue  coming  from  the  pia  mater, 
which  they  have  received  in  their  passage  along  and  through  this 
membrane.  The  connective  tissue  forms  sheaths  around  the  capillary 
network,  arterioles,  and  little  veins,  in  which  the  vessels  seem  to  float. 
These  have  been  termed  the  perivascular  sheaths  of  His.  Between 
them  and  the  vessels  exists  a  lymph-space:  one  of  the  origins  of  the 
lymphatics. 

White-Substance  Formation. — The  white  matter  is  formed  by  the 
bundles  of  white  fibers  covered  by  a  lamellar  investment  of  neuroglia. 
These  bundles  are  separated  from  one  another  by  tracts  of  connective 
tissue  detached  from  the  pia  mater. 

Axis-cylinders  are  also  found,  which  come  from  the  gray  matter. 
Blood-vessels  anastomose  and  run  in  a  course  parallel  with  the  nerve- 
fibers.  This  circulatory  network  likewise  has  a  perivascular  sheath  as 
has  that  in  the  gray  substance. 

Chemical  Properties  of  Nervous  Substance. — The  following  table 
of  Landois  gives  the  percentage  of  the  various  components  of  both 
gray  and  white  matters: — 


CIIKMICAL  COMPOSITION  OF 


Water 

Solids 


GRAY  MATTER. 


WHITE  MATTER. 


81.6  per  cent.          68.4  per  cent. 
18.4         "  31.6         " 


The  solids  consist  of  : — 

Proteids  (globulins) |     55.4  per  cent.          24.7  per  cent. 

Lecithin         17.2  "  9.9  " 

Choi esterin  and  fats 18.7  "  52.1  " 

Cerebrin 0.5  "  9.5  " 

Substances  insoluble  in  ether 6.7  "  3.3  " 

Salts  1.5  "  0.5  " 


406  PHYSIOLOGY. 

In  100  parts  of  ash,  Breed  found  potash,  32;  soda,  11 ;  magnesia, 
2;  lime,  0.7;  Nad,  5;  iron  phosphate,  1.2;  fixed  phosphoric  acid, 
39;  sulphuric  acid,  0.1;  and  silicic  acid,  0.4. 

PROTEIDS  occur  chiefly  as  albumin.  They  are  found  in  the  axis- 
cylinder  and  in  the  substance  of  the  nerve-cells.  Halliburton  finds 
that  the  proteids  exist  as  globulins  and  nucleo-proteids.  Xuclein  oc- 
curs especially  in  gray  matter  because  of  the  presence  there  of  its 
units :  the  nerve-cells.  N eurolceratin  is  a  body  which  contains  a  rela- 
tively large  amount  of  sulphur.  It  occurs  in  the  corneous  sheath  of 
nerve-fibers.  In  the  sheath  of  Schwann  is  found  a  substance  which  is. 
very  similar  to  elastin.  From  the  connective  tissue  of  nerves  may 
be  obtained  gelatin. 

FATS  AND  OTHER  SUBSTANCES  SOLUBLE  IN  ETHER  are  found  more' 
particularly  in  the  white  matter. 

CEREBRIN  is  a  white  powder  composed  of  spherical  granules. 
These  are  soluble  in  hot  alcohol  and  ether,  but  are  insoluble  in  cold 
water. 

Haitai  has  shown  that  lecithin,  when  administered  to  white  rats, 
caused  a  gain  of  60  per  cent,  in  body-weight  compared  with  the  nor- 
mal animal.  Hence  lecithin  is  a  stimulant  of  normal  growth. 

LECITHIN  consists  of  glycerin,  two  of  the  hydroxyl  radicles  of 
which  are  combined  with  a  fatty  acid  and  the  third  one  with  phos- 
phoric acid,  and  this  latter  is  combined  with  a  body  called  cholin, 
Cerebrin  is  a  nitrogenized  body  and  yields  on  hydration  with  an  acid  a 
carbohydrate  which  has  been  identified  as  galactose.  Cerebrin  and 
lecithin  when  combined  form  a  body  called  protagon.  Halliburton 
has  found  cholin  in  the  cerebro-spinal  fluid  and  in  the  blood  in  inflam- 
mations of  the  nervous  system. 

EEACTION. — When  passive,  nerve-tissue  is  neutral  or  feebly  alka- 
line. When  active  or  dead  it  is  said  to  be  acid. 

It  is  found  that  after  death  nerves  have  a  more  solid  consistence. 
Probably  some  coagulation  occurs  which  is  to  be  compared  to  the 
stiffening  of  .muscle.  Simultaneously  there  is  generated  and  liberated 
a  free  acid. 

Mechanical  Properties. — A  remarkable  property  of  nerve-fibers 
is  the  absence  of  elastic  tension  according  to  the  varying  positions  of 
the  body.  Divided  nerves  do  not  retract. 

The  cohesion  of  a  nerve  is  an  important  property.  Oftentimes 
when  a  limb  is  forcibly  torn  from  the  body  the  nerve  still  remains 
intact  (though  considerably  stretched),  while  the  other  soft  tissues 
are  completely  severed.  The  sciatic  nerve  at  the  level  of  the  popliteal 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          4Q7 

space  requires  a  force  equal  to  one  hundred  and  ten  or  one  hundred 
and  twelve  pounds  to  rupture  it ;  the  median  or  ulnar  require  forces 
equal  to  forty  or  fifty  pounds.  The  latter  nerves  will  stretch  six  to 
eight  inches  before  the  point  of  rupture  is  reached.  It  is  upon  the 
knowledge  of  this  fact  that  the  method  of  nerve-stretching  is  em- 
ployed in  some  forms  of  neuralgia. 

Nerve-metabolism. — Some  extractives  are  obtained  which  are  be- 
lieved to  be  decomposition  products  of  the  nerve. 

The  Nerve-centers. — The  nerve-fibers  and  nerve-cells  comprise  the 
essentials  from  which  the  nerve-centers  are  formed;  the  elements 
must,  of  course,  be  held  together  by  enveloping  neuroglia.  The  term 
center  is  merely  applied  to  an  aggregation  of  nerve-cells  which  are  so 
related  to  one  another  as  to  subserve  a  certain  function.  These  cells 
give  off  numerous  processes  whereby  they  are  brought  into  direct 
communication  with  one  another  as  well  as  other  parts  of  the  body. 
These  masses  thus  form  structural  integrations  which  perform  cor- 
responding integral  functions.  If  at  any  time  the  structure  suffers, 
the  function  must  of  necessity  suffer  also. 

The  nerve-centers  comprise  the  spinal  cord,  medulla  oblongata, 
pons  Varolii,  cerebrum,  and  cerebellum. 

COMMON  PROPERTIES. — There  are  certain  properties  which  all 
nerve-centers  seem  to  possess  in  common  and  which  are  of  interest  to 
the  student: — 

1.  They  all  contain  nerve-cells.     These  are  the  real  centers  of 
activity.     They  both  originate  and  conduct  impulses.     Xerve-fibers 
are  almost  exclusively  conductors. 

2.  Nerve-centers  are  capable  of  discharging  reflexes.     They  are 
motor,  secretory,  and  inhibitory  reflexes. 

3.  They  are  the  seat  of  automatic  excitement  when  phenomena 
are   manifested   without   the   application   of   any   apparent   external 
stimulus. 

4.  The  nerve-centers  are  trophic  centers  for  both  their  nerves 
and  the  tissues  supplied  by  them. 

THE  SPINAL  CORD. 
Structure  of  the  Spinal  Cord. 

"  The  key  to  the  study  of  the  central  nervous  system  is  to  remem- 
ber that  it  begins  as  an  involution  of  the  epiblast.  It  is  originally 
tubular  with  a  central  canal  whose  brain-end  is  dilated  into  ventricles. 
In  the  spinal  cord  there  are  three  concentrated  parts :  First,  the 


408  PHYSIOLOGY. 

columnar,  ciliated  epithelium ;  outside  of  this  is  the  central  gray  tube ; 
and,  covering  all,  the  outer  white,  conducting  fibers."  (Hill.) 

The  spinal  cord  is  that  portion  of  the  cerebro-spinal  axis  which 
is  inclosed  within  the  vertebral  canal.  It  extends  in  the  form  of  a 
large,  cylindrical  cord  from  the  upper  level  of  the  atlas  to  the  first  or 
second  lumbar  vertebra.  Above  it  is  continuous  with  the  medulla  ob- 
longata.  Below  it  becomes  conical,  to  terminate  finally  in  a  slender 
filament:  the  filum  terminate.  It  is  attached  to  the  base  of  the 
coccyx.  The  filum  terminale  passes  through  and  is  partly  concealed 
by  the  conical  extremity  of  the  spinal  cord.  The  cone  is  a  mass  of 
nerve-roots  which,  from  its  striking  resemblance  to  a  horse's  tail,  has 
been  termed  the  cauda  equina. 

The  average  length  of  the  spinal  cord  is  eighteen  inches.  In  the 
fcetus  the  cord  extends  the  whole  length  of  the  vertebral  canal.  The 
difference  in  relative  length  of  the  cord  in  the  foetus  and  in  the 
adult  is  due  to  the  unequal  and  more  rapid  growth  of  the  spinal 
canal  than  the  cord.  The  cord  thus  seems  to  ascend  in  its  canal.  In- 
stead of  the  spinal  nerves  of  the  lower  portion  of  the  cord  leaving  their 
points  of  emergence  horizontally,  they  sweep  down  like  the  hairs  in  the 
tail  of  a  horse  to  form  the  aforementioned  cauda  equina. 

Coverings. — Not  only  is  the  cord  protected  by  the  spinal  canal 
in  which  it  is  suspended,  but  in  addition  is  enveloped  by  a  triple 
membranous  container.  The  cord  does  not  more  than  half  fill  the 
lumen  of  the  spinal  canal.  It  is  suspended  in  this  cavity  surrounded 
by  an  aqueous  medium :  the  cerebro-spinal  fluid. 

The  investing  membranes  have  been  termed,  from  within  outward, 
pia  mater,  arachnoid,  and  dura  mater.  They  form  a  sheath,  or  theca, 
which  is  considerably  larger  than  the  cord.  It  is  separated  from 
the  bony  wall  of  the  spinal  canal  by  venous  plexuses  and  loose  areolar 
tissue. 

The  pia  mater  is  a  very  delicate  covering  which  is  closely  adherent 
to  the  cord.  It  sends  numerous  septa  into  the  substance  of  the  cord  as 
well  as  into  its  anterior  and  posterior  median  fissures.  It  is  composed 
of  blood-vessels  and  connective  tissue. 

The  arachnoid  (spider's  web)  is,  as  its  names  implies,  a  very  deli- 
cate, reticular  membrane.  It  is  nonvascular.  Hanging  like  a  curtain 
between  the  innermost  and  outermost  membranes,  it  forms  two  spaces 
which  are  termed  subdural  and  subarachnoid. 

The  outermost  and  toughest  membrane  is  the  dura  mater.  It  is 
a  very  dense  sheath  and  lies  indirectly  in  contact  with  the  canal-wall. 
However,  unlike  the  dura  of  the  brain,  it  does  not  form  the  periosteum 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          4Q9 

for  the  portions  of  the  vertebrae  constituting  the  walls  of  the  spinal 
canal. 

Diameter  of  the  Cord.— The  volume  of  the  cord  is  not  the  same 
throughout  its  whole  extent.  Although  of  a  mean  diameter  of  half  an 
inch,  yet  it  presents  two  decided  enlargements. 

The  one  enlargement  is  at  the  level  of  the  inferior  portion  of  the 
cervical  region;  the  other  at  the  lower  portion  of  the  dorsal  region. 
The  first  one  is  the  cervical  enlargement  from  which  emerge  the  nerves 
of  the  upper  extremities.  The  name  brachial  enlargement  has  been 
given  to  it. 

From  the  lower  enlargement  arise  the  nerves  which  proceed  to 
the  lower  extremities.  It  is  known  as  the  lumbar  enlargement.  At 
the  site  of  each  enlargement  the  cord  loses  its  cylindrical  form  to 
become  somewhat  flattened  from  before  backward. 

The  formation  of  the  enlargements  is  in  intimate  relation  with 
the  development  of  the  members.  In  fishes,  which  have  only  rudi- 
mentary members,  the  cord  is  of  uniform  diameter  throughout.  In 
steelworkers  the  cervical  swelling  is  considerable. 

The  weight  of  the  cord  is  about  one  and  one-fourth  ounces;  it 
is  equal  to  about  one-fortieth  of  the  weight  of  the  brain. 

The  suspension  of  the  spinal  cord  within  the  canal  is  maintained 
antero-posteriorly  by  irregular  fibrous  tracts  which  form  the  liga- 
mentum  denticulatum.  Laterally  the  roots  of  the  spinal  cord  give 
support ;  below  the  filum  terminate  fastens  it  to  the  coccyx ;  above  its 
continuation  as  the  medulla  furnishes  the  most  important  support. 

Exterior  Form  of  the  Cord. — Externally  the  cord  has  two  longi- 
tudinal median  grooves:  one  anterior,  the  other  posterior.  They 
traverse  the  entire  length  of  the  cord  to  divide  it  into  two  halves 
which  are  usually  perfectly  symmetrical.  The  origins  of  the  spinal 
nerves  are  situated  upon  each  side  of  these  two  parallel,  longitudinal 
lines. 

The  anterior  median  groove  divides  the  anterior  surface  of  the 
cord  into  two  perfectly  equal  parts.  It  extends  from  the  decussation 
of  the  pyramids  to  the  caudal  extremity  of  the  cord.  In  depth  it 
occupies  nearly  a  third  of  the  thickness  of  this  organ.  In  this  groove 
is  folded  a  layer  of  pia  mater ;  at  its  base  is  seen  a  layer  which  passes 
from  one-half  of  the  cord  to  the  other — the  white,  or  anterior,  com- 
missure. 

The  posterior  median  fissure,  deeper  and  more  narrow  than  the 
anterior,  extends  from  the  nib  of  the  calamus  scrip  to  rius  to  the  termi- 
nation of  the  spinal  cord.  Into  this  groove  the  pia  mater  sends  but 


410  PHYSIOLOGY. 

a  simple  partition ;  but  it  is  very  adherent  to  the  walls  of  the  groove. 
The  depth  of  the  fissure  is  bounded  by  a  commissure  analogous  to  that 
which  is  furnished  to  the  anterior  median  groove,  but  of  a  gray  color. 
This  is  the  gray,  or  posterior,  commissure. 

Upon  each  side  of  the  cord  are  seen  two  lateral  grooves  which 
represent  the  lines  of  implantation  of  the  anterior  and  posterior  roots. 
They  are  known  as  the  antero-  and  postero-  lateral  grooves.  The  lat- 
ter is  the  more  apparent  of  the  two,  showing  itself  in  the  form  of  a 
dotted,  longitudinal  line. 

The  antero-lateral  groove  corresponds  to  the  line  of  insertion  of 
the  anterior  roots  of  the  spinal  nerves.  The  two  lateral  grooves  may 
be  regarded  as  purely  artificial :  seen  only  after  the  spinal  nerves  are 
torn  from  the  cord. 

By  virtue  of  the  median  and  lateral  fissures  the  cord  is  divided 
into  columns,  paired  and  symmetrical.  The  portion  comprised  be- 
tween the  anterior  median  and  the  antero-lateral  fissures  is  known  as 
the  anterior  column.  That  portion  between  the  two  lateral  fissures 
bears  the  name  of  lateral  column.  That  part  between  the  postero- 
lateral  and  posterior  median  groove  is  the  posterior  column. 

Anatomy  and  physiology  demonstrate  that  the  separation  of  the 
anterior  from  the  lateral  column  is  not  complete;  hence  it  is  cus- 
tomary to  reunite  these  two  columns  under  the  name  of  antero-lateral 
columns. 

Internal  Conformation  of  the  Spinal  Cord. — The  texture  of  the 
cord  is  best  studied  by  means  of  transverse  section.  These  sections 
show  that  the  cord  is  composed  throughout  its  whole  extent  of  two 
substances :  one,  the  cortical,  white  substance;  and  the  other,  the 
central,  gray  substance. 

The  ivhite  substance  is  located  peripherally  and  covers  all  of  the 
gra}^  substance  except  at  the  base  of  the  posterior  median  groove.  It 
forms  the  columns  which  have  just  been  pointed  out. 

The  gray  substance  forms  in  each  half  of  the  cord  a  longitudinal 
column  whose  transverse  section  appears  in  the  form  of  a  crescent  with 
its  concavity  directed  externally.  The  crescent  terminates  in  two 
swollen  extremities,  the  anterior  one  having  the  name  of  anterior 
horn;  the  posterior  one,  that  of  the  posterior  horn. 

The  two  crescents  are  bound  to  one  another  at  their  convexity 
by  the  aid  of  a  transverse  band  of  gray  substance,  the  gray  commissure. 
This  band  is  pierced  centrally  by  a  canal,  the  central  canal  of  the  cord. 
It  runs  down  the  central  axis  of  the  cord  and  is  accompanied  on  each 
side  by  a  vein,  the  central  veins  of  the  cord.  In  all  sections  the  gray 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          41 1 

matter  is  vaguely  represented  by  the  letter  H;  perhaps  better  by  the 
two  wings  of  a  butterfly  united  by  a  transverse  bar.  The  column  of 
gray  matter  is  not  exactly  of  the  same  form  in  its  whole  length.  It 
is  thicker  in  the  cervical  and  lumbar  regions  than  in  the  thoracic. 
The  white  matter  is  likewise  thicker  at  the  level  of  the  cervico-dorsal 
and  lumbar  enlargements.  At  the  level  of  the  cauda  equina  the  white 
substance  forms  but  an  enveloping  layer  for  the  gray  matter. 

In  the  cervical  and  lumbar  regions  the  anterior  cornua  are  re- 
markable for  their  volume;  toward  the  dorso-lumbar  enlargements 
the  posterior  cornua  increase  in  size.  The  anterior  cornu  of  the 
crescent  is  swollen.  The  posterior  is  more  slender  and  reaches  to  the 
surface  of  the  cord.  Each  cornu  possesses  a  swelling  (head)  and  a 
somewhat  restricted  portion  (cervix). 

The  head  of  the  posterior  cornu  is  remarkable  in  that  it  is 
capped  with  a  layer  of  neuroglia  to  which  has  been  given  the  name 
of  gelatinous  substance  of  Rolando.  It  is  nearly  amorphous,  and,  in 
section,,  gives  an  appearance  very  similar  to  the  small  letter  u.  The 
substantia  contains  a  few  neuroglia  cells,  with  some  fusiform  nerve- 
cells  along  its  margin. 

In  the  inferior  cervical  and  superior  thoracic  region  the  most 
lateral  portion  of  the  anterior  cornu  is  shaped  in  a  special  fashion  so  as 
to  constitute  a  particular  prolongation.  This  is  known  as  the  lateral 
cornu,,  or  intermedia-lateral  column.  The  cells  of  this  column  are  ar- 
ranged in  groups  of  from  eight  to  twelve  bipolar  cells  whose  long  axes 
are  vertical  or  more  or  less  oblique.  It  is  believed  that  these  give  origin 
to  those  fine  medullated  fibers  which  form  the  splanchnic  efferent 
fibers. 

On  examination  of  sections  it  is  seen  that  the  anterior  cornua 
do  not  reach  to  the  surface  of  the  cord.  Hence  that  portion  of  the 
white  substance  which  surrounds  the  anterior  cornua  reaches  from 
the  anterior  median  groove  to  the  posterior  cornua.  It  seems  to  form 
a  homogeneous  column :  the  antero-lateral  column. 

In  the  rear,  on  the  contrary,  the  posterior  cornua  sharply  sepa- 
rate the  preceding  to  form  posterior  columns.  They  lie  between  the 
posterior  median  groove  and  the  posterior  cornna.  In  the  cervical 
region  the  posterior  column  is  sharply  divided  into  two  secondary 
columns  by  the  posterior  intermediate  groove.  These  are  the  columns 
of  Goll  (next  to  the  posterior  median  groove)  and  Burdach  (in  appo- 
sition with  the  posterior  cornu). 

From  measurements  by  Stilling  it  seems  that  the  cervical  swell- 
ing results  from  a  localization  of  superdevelopment  of  both  the  gray 


412  PHYSIOLOGY. 

and  the  white  matter  of  the  cord.  The  lumbar  enlargement  is  almost 
exclusively  formed  by  a  localized  superdevelopment  of  gray  substance. 
This  is  readily  explained  by  the  constitution  of  the  columns  them- 
selves. Excepting  the  fibers  forming  the  roots  of  the  spinal  nerves, 
the  columns  of  white  matter  are  formed  of  descending,  or  motor,  and 
ascending,  or  sensory,,  fibers.  The  motor  bundle  successively  gives  off 
fibers  to  the  motor  roots  of  the  spinal  nerves  to  such  a  degree  that  in 
their  descent  their  volume  proportionately  diminishes. 

The  sensory,  or  ascending,  bundle,  receiving  fibers  from  each 
posterior  root  which  comes  from  a  sensory  nerve,  enlarges  as  it 
ascends.  Hence  it  results  that  at  the  level  of  the  lumbar  enlarge- 
ment the  bundles  are  at  a  minimum,  the  ascending  bundle  just  com- 
mencing, while  the  descending  bundle  is  nearly  spent. 

Minute  Constitution  of  the  Cord. — The  spinal  cord  is  composed 
of  fibers,  nerve-cells,  neuroglia,  and  blood-vessels.  In  the  white  sub- 
stance there  are  found  only  nerve-fibers  and  neuroglia;  in  the  gray 
substance,  nerve-cells  and  fibers  plunged  in  a  stroma  of  neuroglia. 

WHITE  SUBSTANCE. — The  white  matter  is  composed  principally 
of  medullated  fibers  without  the  sheath  of  Schwann.  The  fibers  in  the 
white  substance  are,  for  the  most  part,  arranged  longitudinally ;  those 
which  pass  to  the  nerve-roots,  as  well  as  those  fibers  which  proceed  from 
the  gray  matter  into  the  columns,  possess  an  oblique  course.  In  addi- 
tion there  are  decussating  fibers  in  the  white  commissure. 

On  cross-section  the  fibers  (which  are  of  different  sizes)  present 
the  appearance  of  small  circles  with  a  rounded  dark  spot  in  their 
centers.  This  latter  represents  the  axis-cylinder  of  the  fiber. 

The  diameter  of  the  fibers  varies  from  V5ooo  to  V1200  inch  in 
diameter.  The  most  voluminous  are  the  motor  parts  of  the  antero- 
lateral  column  and  direct  cerebellar  tract;  the  finest  are  in  the 
posterior  median  column. 

Classification. — The  fibers  of  the  cord  are  classified  into  two 
great  classes :  intrinsic  and  extrinsic. 

Intrinsic. — This  class  of  fibers  originates  in  and  terminates  in 
the  cord,  thereby  uniting  the  levels  of  gray  matter.  Fixed  by  their 
lower  extremity  upon  a  given  point  of  gray  substance,  they  follow  an 
ascending  course,  to  become  lost  by  their  extremity  in  a  more  or  less 
elevated  part  of  the  gray  column.  Thus  they  are  fibers  of  union  or 
association  for  the  purpose  of  establishing  communication  between 
the  different  levels  of  the  gray  substance  of  the  cord. 

Extrinsic. — These  fibers  in  the  gray  matter  proceed  to  'the  gan- 
glia of  the  brain  after  having  traversed  the  medulla  oblongata, 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          413 

pons,  and  crura.  They  unite  the  cells  of  the  gray  substance  of  the 
spinal  cord  to  the  upper  nerve-centers.  They  are  long  and  gradually 
diminish  in  number  from  the  top  to  the  bottom  of  the  cord. 

Degeneration  occupies  their  whole  extent.  Some  are  centripetal 
and  undergo  an  ascending  degeneration.  They  are  contained  in  the 
column  of  Goll,  the  direct  cerebellar  bundle,  and  Gowers's  tract.  The 
others  are  centrifugal  fibers,  and  undergo  a  descending  degeneration. 
They  are  localized  in  the  crossed  pyramidal  and  bundle  of  Tiirck. 
They  are  the  last  ones  to  appear  in  the  foetus. 

The  roots  of  the  nerves  arrive  at  the  central  gray  substance  and 
plunge  into  it  after  having  passed  between  the  fibers  of  the  peripheral 
white  substance.  But  few  of  them  take  part  in  the  constitution  of 
the  cortical  white  matter. 

Neuroglia. — In  addition  to  the  fibers  just  discussed  the  white 
matter  of  the  cord  contains  neuroglia.  From  the  neuroglia  project 
extremely  fine  prolongations.  These  penetrate  the  cord  to  form 
within  its  thickness  an  infinity  of  partitions  of  extreme  thickness. 
These  are  united  to  the  adventitious  tissue  of  the  vessels  and  to  the 
tissue  which  serves  as  a  basement  membrane  to  the  epithelium  of  the 
ependyma.  Thus  there  is  formed  (on  transverse  section)  a  polygonal 
network  which  isolates  little  colonies  of  nerve  elements  one  from  the 
other.  This  sort  of  framework  has  been  compared  to  a  sponge  in 
whose  interstices  are  found  the  fibers  and  cells  of  the  cord. 

Neuroglia  does  not  belong  to  the  category  of  connective  tissues. 
It  is  a  special  formation  which  is  derived  from  the  primitive  epi- 
blast.  In  the  central  gray  substance  the  neuroglia  does  not  seem 
any  more  than  amorphous  matter  with  some  few  cellular  elements. 
The  gelatinous  substance  of  Rolando  is  composed  of  abundant  neurog- 
lia in  the  form  of  amorphous  matter.  The  only  connective  tissue 
present  in  the  cord  is  carried  in  by  the  blood-vessels. 

GKAY  MATTER  or  THE  CORD. — The  gray  substance  of  the  cord  is 
composed  of  neuroglia,  fibrils, 'and  nerve-cells. 

The  cells  of  the  cord  are  formed  by  a  small  mass  of  protoplasm 
in  which  is  plunged  a  nucleus  surrounded  by  pigment-granules. 
These  cells,  whose  volume  varies  with  the  groups,  have  a  certain 
number  of  prolongations. 

Cell-arrangement. — The  cells  of  the  cord  are  not  disseminated 
in  the  gray  substance  in  a  disorderly  way.  They  are  grouped  at 
certain  points  to  form  nuclei — nuclei  of  nerves;  these  are  situated 
one  above  the  other  in  a  fashion  to  form  columns  parallel  with  the 
long  axis  of  the  cord. 


414  PHYSIOLOGY. 

There  are  distinguished  three  groups  in  the  anterior  horns:  an 
interior  internal  group,  an  anterior  external  group,  and  a  posterior 
external  group. 

In  the  posterior  horns  the  cells  are  fewer  in  number;  it  is  only  at 
the  internal  part  of  the  neck  of  these  horns  that  there  is  found  a 
grouping.  It  is  known  as  the  dorsal  nucleus  of  Stilling  or  the  vesicular 
column  of  Clarke.  The  ganglionic  cells  of  the  anterior  horns  are  very 
large,  star-shaped,  and  from  1/350  to  1/200  inch  in  diameter.  That  is, 
they  are  nearly  large  enough  to  be  visible  to  the  naked  eye. 

Degeneration. — The  nuclei  of  origin  of  the  anterior  roots  arc 
seized  with  degeneration  in  the  various  forms  of  muscular  atrophy. 
The  cells,  by  reason  of  their  function,  are  known  as  motor  cells.  They 
are  motors  for  the  muscles  to  which  their  nerves  go,  and  trophic  for 
the  same  nerves  and  muscles.  Progressive  muscular  atrophy  is  ana- 
tomically characterized  by  a  general  atrophy  of  the  motor  cells  of  the 
anterior  horns  of  the  cord.  Children's  palsy  is  also  characterized  by 
an  inflammation  of  these  cells. 

The  cells  of  the  posterior  horns,  irregularly  distributed  in  the 
neuroglia,  are  fewer  in  number  and  smaller  in  size  than  are  those  of 
the  anterior  horns.  Their  diameters  average  about  1/1200  inch. 

Anatomically,  the  column  of  Clarke  exists  only  from  the  second 
lumbar  to  the  eighth  dorsal  pair  of  nerves.  However,  there  are  small 
erratic  groups  of  cells  and  two  restiform  nuclei  at  the  level  of  the 
medulla  which  are  analogous  to  the  two  columns  of  Clarke.  The  cells 
of  the  column  of  Clarke  are  very  large,  star-shaped,  and  only  very 
meagerly  branched. 

The  intermedio-lateral  gray  column  is  in  the  outermost  portion  of 
gray  matter,  midway  between  the  anterior  and  posterior  horns.  It 
lies  in  what  is  known  as  the  lateral  horn.  It  is  the  spinal  origin  of 
the  great  sympathetic.  The  greater  part  of  the  posterior  root-fibers 
are  said  to  end  in  these  columns.  From  this  as  a  source  fibers  pass 
into  the  column  of  Goll  and  the  direct  cerebellar  tract;  other  fibers 
pass  into  the  columns  of  Burdach  and  Gowers. 

To  the  degenerative  changes  within  the  cells  of  the  column  of 
Clarke  have  been  attributed  the  vasomotor  troubles  of  paralysis 
agitans.  Sclerosis  of  the  lateral  columns  explains  the  exaggerated 
trembling  in  the  reflexes. 

The  fibers  of  the  cells  of  the  gray  matter  form  a  spongy  sub- 
stance which  unites  the  two  halves  of  the  gray  axis  of  the  cord  to  one 
another.  This,  the  gray  commissure,  passes  in  front  of  and  behind 
the  central  canal  of  the  cord. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          415 

Neuroglia. — The  neuroglia  of  the  gray  matter  has  a  structure 
analogous  to  that  of  the  neuroglia  of  the  white  substance  of  the  cord. 
It  is  found  in  particular  abundance  at  the  extremity  of  the  posterior 
horns,  (gelatinous  substance  of  Rolando)  and  at  the  periphery  of  the 
central  canal. 

The  Central  Canal. — This  is  a  canal  of  very  fine  caliber  located 
within  the  center  of  the  gray  commissure.  It  traverses  the  entire 
length  of  the  cord  and,  at  the  level  of  the  nib  of  the  calamus  scrip- 
torius,  is  continuous  with  the  fourth  ventricle ;  by  means  of  the  latter 
it  communicates  with  the  ventricles  of  the  brain. 

The  wall  of  this  canal,  known  as  the  ependyma,  is  composed — 
from  within  outward — of:  (1)  a  ciliated  epithelium,  (2)  an  amor- 
phous basal  membrane,  and  (3)  a  substratum  of  neuroglia  which 
unites  the  wall  of  the  canal  to  the  body  of  the  cord.  The  canal  is 
flanked  on  each  side  by  a  longitudinal  vein;  the  two  constitute  the 
central  veins. 

Systemization  in  the  Spinal  Cord. — The  spinal  cord  may  be  con- 
sidered as  formed  of  a  series  of  segments  superposed.  They  are 
metameres  corresponding  to  each  pair  of  spinal  nerves.  Each  one  of 
these  is  a  complete  center,  being  supplied  with  nerve-cells  and  motor 
and  sensory  nerves.  Each  one  is  different  from  its  neighbor,  since  it 
innervates  a  particular  area  of  the  surface  of  the  body,  whether  it  be 
tactile  surface  or  muscular  group. 

The  nerve-cells  are  grouped  in  motor  and  sensory  fields.  They 
are  all  in  perfect  communication  with  one  another  by  reason  of 
numerous  fibers;  some  are  longitudinal  (longitudinal  commissures) 
which  unite  the  various  levels  of  the  cord;  others  are  transverse 
(transverse  commissures)  whose  function  seems  to  be  to  unite  the 
cells  of  the  right  side  to  those  of  the  left  side  of  each  segment.  The 
transverse  commissures  are  but  from  one  to  three  centimeters  in 
extent. 

In  addition  to  the  spinal  commissures  just  mentioned,  there  are 
two  other  kinds  formed  by  the  long  fibers  uniting  the  spinal  cord 
either  to  the  cerebrum  or  cerebellum.  They  are  known  as  the 
cerebro-spinal  and  cerebello-spinal  fibers. 

Experimental  physiology,  pathological  anatomy,  and  embryology 
all  agree  very  admirably  in  demonstrating  that  the  apparently  homo- 
geneous cord  is  composed  of  distinct  and  specialized  parts.  These 
parts  are  called  systems,  which,  in  the  white  substance,  form  sec- 
ondary columns,  or  bundles. 


416  PHYSIOLOGY. 

White  Columns  of  the  Cord. 

Flechsig  ascertained  that  in  the  foetus  the  different  bundles  of 
nerve-fibers  did  not  all  take  on  myelin  layers  at  the  same  time.  By 
taking  advantage  of  this  fact  he  was  able  to  trace  the  bundles  of  fibers 
with  myelin  and  thus  map  out  the  different  tracts  of  the  spinal  cord 
and  brain.  Gudden  extirpated  an  organ  of  sense  and  after  waiting 
a  sufficient  length  of  time  was  able  to  trace  the  course  of  the  atro- 
phied nerve-fibers. 

The  nerve-fibers  of  the  cord  enveloping  the  central  gray  axis  are 
distributed  in  different  bundles  or  columns.  These  have  previously 
been  mentioned  cursorily,  but  will  now  be  discussed  in  detail. 

Anterior  Column, — The  anterior  column  comprises  that  area  be- 
tween the  anterior  median  groove  and  the  line  of  implantation  of  the 


Fig.  100. — Transverse  Section  of  the  Spinal  Cord. 

T.  B.,  Burdach's  tract.  T.  G.,  Goll's  tract.  T.  P.  C.,  Crossed  pyramidal 
tract.  T.  C.  D.,  Direct  cerebellar  tract.  T.  G.,  Gowers's  tract.  T.  P.  D., 
Direct  pyramidal  tract,  or  Tiirck's.  T.  L.  P.,  Deep  lateral  tract.  Straight 
lines  are  motor  tracts.  Little  crosses  are  sensory  tracts.  Dotted  spaces  are 
cerebellar  tracts.  T.  /.,  T.  R.,  Root  tracts. 

anterior  roots  of  the  spinal  nerves.  Its  most  internal  fibers  are  coni- 
missural;  they  cross  throughout  the  whole  extent  of  the  cord  and  so 
contribute  in  the  formation  of  the  white  commissure.  Other  fibers 
run  across  at  the  same  level  to  connect  the  large  cells  of  the  anterior 
horns  of  the  two  halves  of  the  spinal  cord. 

The  anterior  column  comprehends  two  bundles:  one,  internal 
(next  to  the  median  groove),  is  known  as  Turck's  bundle,  or  direct 
pyramidal  bundle;  the  other,  external,  comprises  the  remainder  of 
the  anterior  column  and  is  known  as  the  root-bundle  of  the  anterior 
column,  or  antero-lateral  ground-bundle. 

The  bundle  of  Tiirck  (pyramidal  bundle,  direct  cerebral,  direct 
motor)  is  formed  of  centrifugal  fibers  which  descend  from  the  brain 
into  the  cord  without  decussating  at  the  level  of  the  medulla  ob- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 

longata.  Its  fibers  are  longitudinal  and  travel  along  and  through 
the  brain,  the  anterior  pyramid  of  the  medulla,  and  the  same  side 
of  the  corresponding  half  of  the  spinal  cord.  Yet,  having  arrived 
in  the  cord,  some  of  its  fibers  cross  to  the  opposite  side  along  the  path 
of  the  white  commissure.  They  finally  terminate  in  the  cells  of  the 
anterior  cornua.  This  bundle  usually  terminates  about  the  second 
lumbar  nerve.  It  undergoes  descending  degeneration. 

The  antero-lateral  ground-bundle  (root-bundle  of  the  anterior  col- 
umn) occupies  the  territory  between  the  preceding  and  the  antero- 
lateral  groove.  It  is  formed  in  part  by  the  anterior  roots  which 
descend  in  a  certain  course  within  its  interior;  but  especially  by  the 
more  or  less  long,  longitudinal  fibers.  The  latter  unite  between 
themselves  the  successive  levels  of  the  anterior  horns.  It  is  thus  in 
part  a  system  of  longitudinal  commissural  fibers. 

Lateral  Column. — The  lateral  column  is  bounded  between  the 
line  of  implantation  of  the  anterior  roots  and  the  line  of  insertion 
of  the  posterior  roots.  It  is  formed  of  fibers  which  are  larger  on  the 
surface  and  much  finer  in  the  depths. 

This  column  comprises  five  different  systems  of  bundles.  They 
are :  (1)  the  direct  cerebellar;  (2)  the  bundle  of  Gowers,  or  ascending 
antero-lateral  cerebellar  tract;  (3)  the  crossed  pyramidal  tract;  (4) 
tract  of  Loewenthal,  or  descending  antero-lateral  cerebellar  tract;  (5) 
deep  lateral,  or  lateral  marginal,  zone. 

The  direct  cerebellar  bundle,  or  tract,  is  situated  at  the  posterior 
and  superficial  part  of  the  lateral  column  in  the  form  of  a  very  thin 
band.  It  extends  from  the  second  lumbar  upward  to  the  restiform 
bodies,  into  the  vermis  of  the  cerebellum.  It  is  formed  of  a  ^collec- 
tion of  centripetal  fibers  which  unite  the  cerebellum  to  different 
levels  of  the  vesicular  column  of  Clarke.  It  develops  ascending  de- 
generation. About  the  cells  of  Clarke  arborize  the  collaterals  of  the 
posterior  root  so  that  there  is  an  indirect  communication  between  the 
posterior  roots  and  the  cerebellum. 

The  bundle  of  Gowers,  or  ascending  antero-lateral  tract,  occupies 
the  anterior  superficial  zone  of  the  lateral  column.  This  bundle  com- 
mences at  its  inferior  part  in  the  lumbar  swelling,  increasing  in  size 
as  it  ascends  by  two  orders  of  roots,  some  fine,  others  large.  It  termi- 
nates by  its  fine  fibers  in  the  lateral  nucleus  of  the  medulla;  by  its 
larger  fibers  in  the  cerebellum  by  way  of  the  superior  peduncle.  This 
tract  undergoes  ascending  degeneration. 

The  crossed  pyramidal  tract  (motor  tract  or  cerebral  crossed 
tract)  is  situated  inside  the  cerebellar  tract.  The  term  has  been 

27 


418  PHYSIOLOGY. 

applied  to  that  which  is  contained  within  the  pyramids  of  the 
medulla,  and  which  decussates  at  this  level  with  the  opposite  tract. 
It  decreases  in  volume  from  above  downward  to  terminate  in  from 
the  second  to  the  fourth  lumbar  pair. 

It  is  composed  of  long,  centrifugal  fibers  which  unite  the  motor 
regions  of  the  cortex  of  the  brain  with  the  motor  cells  of  the  anterior 
horns  of  the  cord.  It  undergoes  descending  degeneration  as  the  re- 
sult of  lesions  which  seize  the  cortex,  internal  capsule,  or  cerebral 
peduncle. 

A  lesion  of  the  pyramidal  tract  in  the  cord  produces  hemiplegia 
or  monoplegia  below  the  lesion  and  on  the  same  side.  Its  degenera- 
tion, as  a  result  of  lesion  of  the  brain,  gives  place  to  a  crossed  hemi- 
plegia, whose  clinical  mark  is  a  spasmodic  contracture. 

It  is  well  to  remember  that  there  is  a  double  decussation  of  the 
motor  fibers:  one  at  the  level  of  the  neck  of  the  medulla  oblongata, 
the  other  much  lower — the  length  of  the  white  commissure.  From 
this  the  student  can  comprehend  why  in  the  majority  of  hemiplegias 
the  nonparalyzed  member  has,  nevertheless,  lost  its  muscular  energy; 
also  why  a  unilateral  cerebral  lesion  is  able  to  cause  permanent  con- 
tracture of  the  two  inferior  members  or  an  exaggeration  of  the  re- 
flexes of  the  side  not  paralyzed. 

The  bundle  of  Loewenthal  and  Marchi,  or  antero-lateral  de- 
scending cerebellar  tract,  comes  from  the  cerebellum  of  the  same 
side  by  the  inferior  cerebellar  peduncle.  The  fibers  form  an  extensive 
circumferential  tract  in  the  anterior  three-fourths  of  the  antero- 
lateral  column,  spreading  inward  to  the  intermedio-lateral  column  of 
gray  niatter,  and  run  down  to  the  sacral  cord,  gradually  decreasing 
in  their  descent.  Its  fibers  are  mingled  with  those  of  Gowers's 
column. 

The  deep  lateral  tract,  lateral  mixed  tract,  or  lateral  marginal 
zone,  is  molded  upon  the  lateral  concavity  of  the  gray  matter.  It 
incloses  at  the  same  time  the  fibers  coming  from  the  anterior  motor 
horns,  the  gray  column  of  Clarke,  and  the  gray  intermedio-lateral 
column. 

Posterior  Columns. — The  posterior  columns  comprise  that  area 
of  the  spinal  cord  lying  between  the  postero-lateral  groove  and  the 
posterior  median  groove.  It  is  composed  of  fine  fibers  in  that  portion 
nearest  the  median  groove,  and  is  remarkable  for  its  abundance  of 
neuroglia. 

This  large  tract  is  divided  into  two  tracts :  one  internal,  the  other 
external. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          419 

The  internal  one,  or  column  of  Goll,  is  especially  apparent  in  the 
upper  part  of  the  cord.  Here  it  occurs  in  the  form  of  a  triangular 
pyramid  whose  base  is  turned  toward  the  central  gray  commissure. 
It  is  formed  by  long  commissural  fibers  which  arch  so  as  to  unite  the 
posterior  horns.  They  proceed  from  the  level  of  one  posterior  horn 
to  that  of  a  higher  level.  It  incloses  the  posterior  root-fibers  which 
compose  the  major  portion  of  it.  The  fibers  of  the  column  of  Goll  are 
very  long,  ascending  from  the  cauda  equina  to  the  nucleus  of  this 
tract  in  the  medulla.  Its  trophic  centers  are  in  the  cells  of  the  pos- 
terior horns. 

The  more  external  and  cuneiform  tract,  column  of  Burdach,  con- 
tains short,  commissural,  longitudinal  fibers  which  have  the  same  dis- 
tribution as  those  of  Goll,  and  sensory  fibers,,  which  also  spring  from 
the  posterior  horns,  but  do  not  sojourn  there.  Almost  immediately 
they  pass  into  the  mixed  lateral  column  of  the  same  side,  or,  travers- 
ing the  commissure,  cross  into  the  opposite  tract.  At  the  level  of 
the  medulla  oblongata  these  fibers  go  to  form  the  lemniscus,  or  fillet, 
which  itself  terminates  in  the  corpora  quadrigemina,  optic  thalami, 
and  the  sensory  convolutions.  In  transverse  section  of  the  cord  there 
is  ascending  degeneration. 

The  comma  tract  is  composed  of  a  few  fibers  in  the  column  of 
Burdach.  After  lesions  of  the  cord  they  undergo  descending  de- 
generation. These  fibers  originate  from  the  descending  fibers  of  the 
posterior  roots. 

The  posterior  columns,  and  particularly  the  columns  of  Burdach, 
are  the  seat  of  the  sclerosis  known  as  tabes  dorsalis,  or  locomotor 
ataxia.  Clinically  this  disease  is  characterized  by  progressive  aboli- 
tion of  co-ordination,  loss  of  equilibrium,  paralysis  of  eye-muscles, 
loss  of  tendon  reflexes,  etc. 

Tracts  of  Lissauer. — About  the  entrance  of  the  posterior  roots 
into  the  postero-lateral  groove  of  the  cord  are  found  two  small, 
cuneiform  columns.  They  are  the  root-zones  of  Lissauer.  The  one 
is  internal,  the  other  external.  The  two  zones  are  formed  by  the 
posterior  root-fibers  at  their  entrance  into  the  cord.  They  have  the 
same  properties  as  the  posterior  roots  and  undergo  ascending  de- 
generation under  the  same  conditions  that  produce  it  in  the  latter. 

Roots  of  Nerves. 

The  spinal  nerves,  thirty-one  pairs  in  number,  exist  throughout 
the  entire  length  of  the  cord. 


420  PHYSIOLOGY. 

The  anterior  root-fibers  are  composed  of  large  nerve-tubes  which 
lose  themselves,  for  the  most  part,  in  the  ganglionic  cells  of  the 
anterior  horns  of  the  same  or  opposite  sides. 

The  posterior  root-fibers  are  composed  of  fine  tubes.  After  having 
arisen  in  the  intervertebral  ganglia  they  go  toward  the  postero-lateral 
groove,  where  they  enter  the  cord.  There  are  here  two  groups  of 
fibers :  one  external,  the  other  internal. 

The  external  root-fibers  penetrate  into  the  gelatinous  substance 
of  Rolando,  where  they  become  ascending.  After  a  more  or  less 
lengthy  course  they  pass  into  the  ganglionic  cells  of  the  posterior 
horn. 

The  internal  root-fibers,  which  pass  into  the  posterior  column,  be- 
come lost  either  in  the  cells  of  the  posterior  horn  or  in  the  vesicular 
column  of  Clarke.  Some  very  long  fibers  ascend  to  the  nuclei  of  (roll 
and  Burdach  in  the  medulla,  where  they  terminate. 

Some  of  the  fibers  traverse  the  posterior  commissure  to  pass 
either  into  the  anterior  horn  of  the  opposite  side  (and  so  belong  to 
reflex  motor  actions)  or  into  the  posterior  horn  or  descend  in  the  cord 
as  fibers  of  the  comma  tract. 

Commissures  of  the  Cord. 

The  white,  anterior  commissure  is  formed  by  a  body  of  fibers 
which  decussate  upon  the  median  line  to  pass  into  the  lateral  half 
of  the  cord  opposite  to  that  from  which  they  came.  It  forms  the 
major  portion  of  the  fibers  of  the  direct  pyramidal  tract.  This  tract 
in  its  long  course  in  the  cord  gives  off  fibers  in  succession  which  go 
either  into  the  cells  of  the  anterior  horn  or  into  the  crossed  pyramidal 
tract  of  the  opposite  side.  The  commissure  also  contains  fibers  which 
unite  transversely  the  anterior  horns  of  the  two  sides. 

The  gray,  or  posterior,  commissure  is  likewise  formed  by  decussa- 
tions  upon  the  median  line  both  in  front  of  and  back  of  the  central 
canal.  The  fibers  comprising  this  decussation  are :  some  of  the  fibers 
from  the  posterior  roots  on  one  side  to  terminate  in  the  opposite 
posterior  horn;  also,  fibers  of  the  posterior  horn  which  go  into  the 
deep  lateral  tract. 

MEDULLA  OBLONGATA. 

The  medulla  oblongata  is  a  continuation  of  the  spinal  cord 
which  crowns  its  upper  part  in  the  form  of  a  capital.  It  reaches 
from  the  cord  to  the  pons  Varolii.  The  medulla  is  an  enlargement 
in  the  form  of  a  truncated  cone,  a  little  flattened  from  before  back- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


421 


ward.  It  measures  an  inch  in  length,  about  three-fourths  in  width, 
and  about  one-half  inch  in  thickness.  Commencing  toward  the  mid- 
dle part  of  the  odontoid  process,  it  inclines  forward,  to  recline  upon 
the  basilar  process  of  the  occipital  bone.  The  medulla  forms  with  the 
cord  an  obtuse  angle  open  in  front.  The  back  and  sides  of  the 
medulla  are  embraced  by  the  cerebellum.  In  front,  the  medulla  is 
bounded  anteriorly  by  the  pons  Varolii,  posteriorly  by  a  transverse 


Fig.  101.— Medulla  Oblongata,  Pons,  Cerebellum,  and  Pes  Pedunculi.    Anterior 
View,  to  Demonstrate  Exits  of  Cranial  Nerves.     (EDINGER.) 


line  which  unites  the  lateral  angles  of  the  fourth  ventricle  to  divide 
its  floor  into  two  triangles. 

The  anterior  and  posterior  median  fissures  of  the  cord  are  con- 
tinued up  into  the  medulla.  The  anterior  fissure  becomes  somewhat 
indistinct  at  one  point  by  reason  of  the  decussation  of  the  bundles 
forming  the  pyramids.  The  posterior  median  fissure  terminates  at 
the  lower  end  of  the  fourth  ventricle.  The  weight  of  the  medulla  is 
about  one  hundred  grains. 

From  the  front  and  sides  of  the  medulla  arise  the  sixth  to  the 
twelfth  cranial  nerves,  inclusive. 


422  PHYSIOLOGY. 

External  Form  of  the  Medulla  Oblongata. — Inspection  of  the 
inferior  surface  of  the  medulla  brings  to  view  first  along  the  median 
line  the  anterior  median  groove.  This,  as  before  mentioned,  is  a  con- 
tinuation of  a  similar  groove  belonging  to  the  cord.  In  one  area 
the  crossing  of  the  white  fibers  from  side  to  side  (decussation  of  the 
pyramids)  renders  this  more  shallow.  At  the  base  of  the  groove  is 
seen  a  continuation  of  the  white,  anterior  commissure  of  the  cord. 
This  layer  unites  the  two  pyramids  of  the  medulla  and  is  known  as 
the  raphe  of  Stilling. 

ANTERIOE  PYKAMIDS. — On  each  side  of  the  median  groove  are 
located  two  white  columns,  which  are  slightly  enlarged  at  their  upper 
ends  and  have  the  appearance  of  clubs.  These  columns  are  the  an- 
terior pyramids. 

OLIVES. — Just  outside  of  the  upper  portion  of  the  pyramids  are 
two  prominent,  oval  masses  whose  longer  axes  are  vertical.  These 
bodies  measure  about  one-half  inch  in  length  and  one-fourth  in 
breadth.  They  are  the  inferior  olives.  They  are  prominences  added 
to  the  medulla,  and  do  not  have  any  similar  portions  in  the  spinal 
cord.  The  olives  are  separated  from  the  pyramid  in  front  by  a 
groove;  in  this  latter  is  embodied  the  continuation  of  the  false 
antero-lateral  groove.  In  it  is  found  the  apparent  origin  of  the 
hypoglossal  nerve.  Behind,  the  olives  are  separated  from  the  resti- 
f  orm  bodies  by  another  groove :  a  continuation  of  the  postero-lateral 
groove  of  the  spinal  cord.  From  it  emerge  the  glosso-pharyngeal, 
vagus,  and  spinal  accessory.  At  their  lower  edge  these  grooves  are 
somewhat  effaced  by  the  white  arcuate  fibers  of  the  olive ;  these  latter 
ascend  in  the  restiform  bodies. 

KESTIFOKM  BODY. — Back  of  the  postero-lateral  groove  of  the 
medulla,  and  therefore  on  its  posterior  surface,  is  found  a  large 
column  of  white  substance :  the  restiform  body.  It  seems  to  be  con- 
tinuous below  with  the  posterior  columns  of  the  cord;  above  with 
the  inferior  peduncle  of  the  cerebellum.  These  columns  form  part 
of  the  anterior  as  well  as  lateral  aspects  of  this  organ. 

Posteriorly  it  is  seen  that  the  inferior  third  of  the  medulla  is 
very  different  to  the  upper  two-thirds.  The  inferior  third  is  similar 
to  the  cord  in  that  it  possesses  a  posterior  median  groove  continuous 
with  that  of  the  cord;  on  each  side  of-  it  are  two  white  columns. 
They  are  continuations  of  the  posterior  columns  of  the  cord. 

At  the  base  of  the  groove  is  found  the  gray  commissure. 

In  the  upper  two-thirds  of  the  medulla  this  form  is  much 
changed.  Here  the  posterior  columns  take  the  name  of  restiform 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  .SYSTEM. 


423 


bodies,  or  inferior  peduncles  of  the  cerebellum.  Instead  of  pursuing 
a  parallel  course,  they  diverge  from  one  another  in  such  a  manner  as 
to  leave  between  them  at  their  upper  end  a  V-shaped  surface.  The 
surface  included  within  this  angular  space  comprises  gray  matter. 
It  forms  the  lower  half  of  the  floor  of  the  fourth  ventricle.  The 
upper,  angular  portion  is  formed  by  the  posterior  face  of  the  pons. 

The  beginning  of  divergence  of  the  restiform.  bodies  presents  an 
appearance  analogous  to  that  of  a  writing  pen;  hence  its  name: 
calamus  scriptorius.  The  space  between  the  restiform  bodies  presents 
a  median  groove.  Above  it  passes  over  the  posterior  face  of  the  pons; 


Fig.  102.— The  Three  Pairs  of  Cerebellar  Peduncles.     (After 
HIRSCHFELD  and  LEVEILLE.) 

1,  Fossa  rhomboidalis.  2,  Striae  acusticae.  3,  Posterior  cerebellar  pedun- 
cle. 5,  Anterior  cerebellar  peduncle.  6,  Fillet.  7,  Middle  cerebellar  peduncle, 
or  Brachium  pontis.  8,  Corpora  quadrigemina. 

below  it  is  arrested  by  the  point  of  divergence  of  the  restiform  bodies. 
This  is  known  as  the  groove  of  the  calamus  scriptorius.  From  each 
side  of  this  groove  there  proceed  white  transverse  fibers  whose  direc- 
tion is  at  right  angles  to  that  of  the  groove.  They  are  known  as  the 
bat-bee  of  the  calamus,  or  auditory  strict.  These  fibers  are  the  posterior 
roots  of  the  auditory  nerve. 

The  restiform  bodies,  which  seem  to  form  the  limits  of  the  floor 
of  the  fourth  ventricle  on  each  side  of  the  calamus  scriptorius,  come 
up  from  the  posterior  columns  of  the  cord.  They  ascend  upward  and 
outward  toward  the  cerebellum. 


424  PHYSIOLOGY. 

The  columns  of  Goll  and  Burdach  of  the  spinal  cord  as  they 
enter  the  lower  portion  of  the  posterior  aspect  of  the  medulla  seem 
to  be  divided  into  several  distinct  tracts.  .  Bordering  upon  the  pos- 
terior median  fissure  is  the  funiculus  gracilis  (column  of  Goll).  As 
the  tract  approaches  the  fourth  ventricle  it  broadens  out  to  form  the 
expansion  known  as  the  clava.  The  two  clavse  diverge  to  form  the 
nib  of  the  calamus  scriptorius. 

Lying  external,  but  adjacent,  to  the  funiculus  gracilis  is  another 
tract  which  is  a  continuation  of  the  column  of  Burdach.  It  is  the 
funiculus  cuneatus. 

As  previously  stated,  the  upper,  expanded  portion  of  the  gracilis 
has  been  termed  the  clava;  the  upper  portion  of  the  cuneatus  is 
known  as  the  cuneate  tubercle.  Both  prominences  are  caused  by 
underlying  masses  of  gray  matter. 

The  scriptorial  half  of  the  floor  of  the  fourth  ventricle  is  divided 
into  two  lateral  halves  by  a  longitudinal  groove.  In  each  half  can 
be  seen  three  small  prominences  whose  general  shape  is  somewhat 
triangular.  The  first  one,  a  triangle  of  white  color,  is  the  trigonum 
hypoglossi;  it  covers  the  nucleus  of  origin  of  the  hypoglossus  nerve. 
The  second  one,  the  trigonum  vagi  and  the  continuation  of  the  head 
of  the  anterior  horn,  corresponds  to  the  nuclei  of  the  ninth,  tenth, 
and  eleventh  cranial  nerves.  It  is  the  ala  cinerea.  The  third  emi- 
nence, the  trigonum  acustici,  covers  the  nucleus  of  the  eighth  nerve. 

Internal  Structure  of  the  Medulla. — The  medulla  oblongata,  like 
the  spinal  cord,  is  formed  of  nerve-cells,  nerve-fibers,  and  a  meshwork 
of  neuroglia.  As  it  is  a  continuation  of  the  cord,  one  ought  to  find 
the  white  columns  and  central  axis  common  to  the  spinal  cord.  As 
a  matter  of  fact,  the  constituent  elements  of  the  cord  are  found  in 
the  medulla,  but  their  position  is  changed  very  much.  The  cells 
forming  the  nuclei  of  nerves  are  analogous  to  those  of  the  cord,  but 
are  more  isolated.  They  also  give  exit  to  fibrils  which  unite  them  to 
other  cells  in  the  opposite  half  of  the  medulla  and  in  the  brain 
proper,  and  to  nerves  of  which  they  are  the  seat  of  origin.  In  the 
medulla  the  grouping  of  these  nuclei  is  quite  different  to  that  found 
in  the  spinal  cord.  However,  it  is  always  the  same  central  gray  sub- 
stance, but  modified  in  its  form  and  arrangement.  The  gray  matter 
is  cut  here  and  there  by  white  columns  and  their  fragments. 

To  understand  this  new  disposition  of  the  gray  matter  it  is 
necessary  to  recall  that  at  the  level  of  the  medulla  the  central  gray 
substance  of  the  cord  has  been  pushed  backward  by  reason  of  several 
factors.  These  are :  the  separation  of  the  restif orm  bodies,  the  pas- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          435 

sage  outward  of  the  posterior  columns,  and  the  formation  of  the 
rhomboid  sinus.  The  latter  is  so  arranged  as  to  form  the  floor  of  the 
fourth  ventricle.  The  posterior  horns  have  become  separated  and 
are  so  rotated  upon  themselves  as  to  be  thrown  outward  and  so  placed 
at  the  external  part  of  the  fourth  ventricle.  The  anterior  cornua 
have  their  bases  placed  upon  the  floor  of  the  fourth  ventricle  on  each 
side  of  the  median  raphe. 

The  isolated  horn  of  gray  matter  is  afterward  known  as  the 
nucleus  lateralis. 

Further,  the  crossed  pyramidal  tracts  of  fibers  are  carried  for- 
ward, outward,  and  upward.  By  the  oblique  passage  of  these  numer- 
ous white  fibers  through  the  gray  matter  of  the  anterior  horn  the 
anterior  horn  is  broken  up  so  that  the  caput  is  entirely  separated 
from  the  remainder  of  the  gray  matter.  The  fibers  in  passing  through 
the  base  of  the  anterior  horns  to  decussate  upon  the  median  line  with 
those  of  the  opposite  side  give  rise  to  the  reticulated  formation  of 
Deiters  and  to  the  raphe  of  Stilling. 

FOKMATIO  EETICULARIS. — The  formatio  reticularis  is  an  asso- 
ciated system  of  the  short  fibers  with  nerve-cells  which  is  to  be  met  with 
at  any  point  between  the  spinal  cord  and  the  optic  thalamus.  These 
fibers  run  at  right  angles  to  one  another.  It  is  the  result  of  the  decussa- 
tion  of  the  crossed  pyramidal  and  arciform  fibers  which,  in  their  march 
forward  and  upward,  travel  through  the  base  of  the  anterior  horns  in 
the  form  of  a  multitude  of  small  bundles.  These  arch  and  decussate 
from  side  to  side. 

Still  higher  up  the  fillet  decapitates,  as  it  were,  the  posterior 
horns.  The  caput  comes  close  to  the  surface,  where  it  forms  the 
distinct  projection  known  as  the  gelatinous  substance  of  Rolando. 
The  cervix  of  the  cornu  becomes  broken  up  in  a  manner  similar  to 
that  of  the  anterior  base. 

White  Substance  of  the  Medulla. — This  is  formed  by  the  pro- 
longation of  the  columns  of  the  spinal  cord  and  by  an  additional 
white  mass,  the  olive. 

WHITE  COLUMNS.  —  The  direct  pyramidal  tract,  whose  fibers 
decussate  the  length  of  the  cord  by  traversing  the  white  commissure, 
do  not  cross  at  the  level  of  the  medulla.  They  pass  directly  into  this 
organ,  to  be  placed  in  the  anterior  pyramid  of  the  corresponding  side. 
At  the  level  of  the  medulla  the  two  principal  anterior,  columns,  those 
of  the  right  and  left,  which  heretofore  pursued  a  parallel  course,  now 
separate  from  the  median  line.  They  carry  themselves  outward  and 
backward  for  a  little  distance,  then  bend  inward  to  pursue  a  parallel 


426  PHYSIOLOGY. 

course  again.  By  this  course  there  is  formed  a  sort  of  elliptical  but- 
tonhole which  is  inclined  obliquely  from  bottom  to  top.  Traversing 
this  buttonhole  are  found  the  crossed  pyramidal  bundles;  both  are 
carried  toward  the  median  line,,  where  they  decussate  with  their 
similars  of  the  opposite  side  to  produce  the  pyramidal  decussation. 
Thus,,  the  two  principal  bundles  of  the  anterior  columns  have  become 
posterior  in  the  medulla,  where  they  are  placed  in  the  deepest  part 
of  the  pyramids. 

LATEEAL  COLUMNS.  —  The  crossed  pyramidal  bundle  in  the 
medulla  bends  toward  the  median  line.  Here  it  meets  its  fellow  of 
the  opposite  side,  with  which  it  decussates  in  the  manner  of  a  twist 
to  arrive  in  the  opposite  side  of  the  medulla.  At  this  level,  in  the 
same  pyramid  of  the  medulla,  there  exist  side  by  side  the  direct 
pyramidal  column  of  the  same  side  of  the  cord  and  the  crossed  pyram- 
idal bundle  of  the  opposite  side.  These  two  bundles  now  form  one 
and  the  same  group  of  nerve-fibers.  This  type  of  fibers  forms  the 
pyramidal,  or  cerebral  motor,  tract.  Along  this  course  descend 
motor  messages  to  the  voluntary  muscles  from  the  brain  to  the  an- 
terior horns  of  the  cord,  and  then  along  axis-cylinders  to  the  motor 
plates  in  muscles. 

An  act  incited  by  an  impulse  traveling  along  this  course  is  always 
crossed,  since  the  left  hemisphere  of  the  brain,  for  example,  carries 
the  order  of  motor  power  to  the  right  half  of  the  spinal  cord  by  the 
crossed  pyramidal  fibers  and  to  the  left  half  of  the  spinal  cord  by 
the  direct  pyramidal  tract.  The  latter  tract  decussates  throughout 
the  length  of  the  cord  with  its  f  ellow  of  the  opposite  side.  Thus,  the 
result*  is  that  the  decussation  is  total  for  the  pyramidal  tract  in  its 
complete  action,  and  that  all  of  the  voluntary  parts  excited  from 
some  part  of  the  cerebral  hemisphere  end  in  muscles  of  the  opposite 
side  of  the  body.  From  this  the  student  will  deduce  that  lesions 
which  affect  the  pyramidal  tract  above  the  medulla  oblongata  have 
as  their  direct  result  a  motor  paralysis  opposite  to  the  lesion;  in 
other  words,  a  crossed  hemiplegia. 

POSTERIOE  COLUMNS. — The  columns  of  Goll  ascend  to  the  me- 
dulla, where  they  pass,  without  decussation,  into  the  postpyramidal 
nucleus,  or  nucleus  of  Goll.  By  this  nucleus  it  is  carried  into  the 
cerebellum,  following  part  of  the  restiform  body;  another  part  is 
placed  in  relation  with  the  nuclei  of  the  pons. 

The  column  of  Burdach  comprises  the  longitudinal  commissural 
fibers,  the  root-fibers  of  the  posterior  roots,  and  the  sensory  fibers 
issuing  from  the  column  of  Clarke.  The  root  fibers  and  commissural 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


42? 


fibers  pass,  without  decussation,  into  the  restiform  nucleus,  or  nucleus 
of  Burclach. 

Parts  added  to  the  medulla  oblongata,  which  are  not  found  in 
the  cord,  are :  arcuate  filters  and  olives. 

Arcuate  filters  are  the  curved  fibers  which  are  seen  in  transverse 
section  of  the  medulla.  By  reason  of  their  position  they  have  been 
termed  superficial  and  deep.,  or  external  and  internal. 


Fig.  103. — Cross-section  of  the  Oblongata  through  the  Decussation 
of  the  Pyramids.     (After  HENLE.) 

Fpy,  Pyramidal  tract.  Cga,  Anterior  horn.  Fa',  Remnant  of  anterior 
column.  yg,  Nucleus  funiculi  gracilis.  g,  Substantia  gelatinosa.  XI,  Nervus 
accessorius. 

The  superficial  arcuate  fibers  form  a  more  or  less  voluminous 
ribbon.  They  are  fibers  which  come  from  the  cells  in  GolFs  and 
BurdaclVs  nuclei.  They  proceed  to  the  restiform  body  of  the  same 
side  and  thence  to  the  cerebellum. 

The  internal  arcuate  fibers  likewise  proceed  from  the  cells  of  the 
nuclei  of  Goll  and  Burdach.  The  hindmost  fibers  form  the  sensory 
decussation  of  the  fillet.  Other  fibers  cross  the  median  raphe  in  the 
substance  of  the  medulla,  then  to  pass  upward  into  the  brain. 


428  PHYSIOLOGY. 

The  olivary  body  is  formed  by  a  portion  of  the  white  cortical 
substance  which  belongs  to  the  lateral  column,  by  a  layer  of  inter- 
vening gray  matter  folded  upon  itself,  the  corpus  dentatum,  ia  such 
a  manner  as  to  represent  an  oblong  purse.  This  is  open  at  its  internal 
aspect,  and  is  known  as  the  hilus  of  the  olive.  The  corpus  dentatum 
of  the  olive  is  formed  by  a  great  quantity  of  small,  multipolar  cells. 
The  fibers  which  emanate 'from  it  go  to  the  olive  of  the  opposite 
side,  traversing  the  raphe  or  mounting  toward  the  pons. 

PONS  VAROLII. 

The  pons  is  a  mass  of  nervous  tissue  placed  transversely  and  in 
the  form  of  a  half -ring.  It  is  situated  between  the  medulla  oblongata 
and  cerebral  peduncles,  which  limit  it  below  and  above,  respectively. 
The  cerebellar  hemispheres  bound  it  laterally.  Its  weight  is  sixteen 
or  seventeen  grams. 

For  examination  microscopically  the  pons  presents  six  surfaces 
or  faces. 

1.  The  anterior  face  is  free,  convex,  and  rounded,  and  rests  upon 
the  basilar  gutter  of  the  occipital  bone.    It  presents  an  antero-pos- 
terior  median  depression:    the  basilar  groove.     On  each  side  of  this 
are  two  parallel  prominences  due  t6  the  heaving  up  of  the  annular 
fibers  by  reason  of  the  anterior  pyramids  which  pass  through  it. 

Upon  this  face  are  seen  the  transverse  fibers  which  pass  laterally 
to  penetrate  into  the  corresponding  hemisphere  of  the  cerebellum. 
They  thus  form  a  large  column  upon  each  side,  known  as  the  middle 
cerebellar  peduncles. 

2.  The  posterior  face  forms  part   of  the  floor  of  the  fourth 
ventricle,   and  is  continuous  with   the   corresponding  face   of   the 
medulla  oblongata.    It  forms  a  triangle  whose  apex,  turned  upward, 
is  placed  at  the  level  of  the  lower  orifice  of  the  aqueduct  of  Sylvius. 
The  sides  of  this  triangle  are  formed  by  the  superior  cerebellar  pe- 
duncles.    Upon  the -median  line  it  has  a  groove  which  follows  that  of 
the  calamus  scriptorius.     Upon  each  side  there  are  two  slight  depres- 
sions: one  known  as  the  superior  fovea,  the  other  the  locus  cceruleus. 

3.  A  superior  face. 

4.  The  inferior  face  is  continuous  with  the  base  of  the  medulla 
oblongata.     The  annular  fibers  of  the  pons  embrace  as  a  half-circle 
the  anterior  pyramids  of  the  medulla  oblongata. 

The  two  lateral  faces  (5  and  6)  are  mingled  with  the  origin  of 
the  middle  cerebellar  peduncles.  The  peduncles  sink  into  the  hemi- 
spheres of  the  cerebellum,  where  they  are  lost. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


429 


Structure  of  the  Pons. — The  pons  is  composed  of  nerve-fibers 
and  scattered  nerve-cells.  It  forms  a  kind  of  knot  into  which  con- 
verge the  fibers  coming  from  the  cerebellum,  as  well  as  those  passing 
to  and  fro  from  the  medulla  into  the  cerebral  peduncles. 


Fig.  104.— The  Base  of  the  Brain.     The  Left  Lobus  Temporalis  is  in  part  Repre- 
sented as  Transparent  in  order  that  the  Entire  Course  of  the 
Optic  Tract  might  be  Seen.     (EDINGER.) 

The  transverse  fibers  which  form  the  cortex  of  this  organ  go  in 
great  part  to  the  middle  cerebellar  peduncles.  They  are  the  com- 
missural  fibers  which  unite  one  cerebellar  hemisphere  to  the  other. 


430  PHYSIOLOGY. 

Some  fibers  emanate  from  the  middle  cerebellar  peduncles  and 
decussate  on  the  median  line  with  those  of  the  opposite  side.  They 
thus  form  the  median  raphe.  They  terminate  in  the  gray  masses  of 
the  pons. 

Other  fibers,  having  decussated,  bend  upward  and  ascend  into 
the  cerebral  peduncles.  All  of  the  various  fibers — semi-annular, 
horizontal,  and  oblique — cover  in  the  longitudinal  fibers  which  unite 
the  medulla  oblongata  to  the  cerebral  peduncles.  In  them  various 
planes  are  formed:  (1)  there  is  a  superficial  plane,  or  stratum  zonale, 
which  covers  the  two  pyramidal  columns;  (2)  the  stratum  profundum, 
which  separates  the  pyramids  from  the  fillet  and  upper  part  of  the 
pons;  (3)  the  third  plane,  stratum  complexium,  separates  the  cerebral 
tracts.  It  is  this  separation  which  gives  rise  to  the  formatio  reticu- 
laris  of  the  pons  and  which  is  continuous  with  the  formatio  reticularis 
of  the  medulla. 

Between  the  superior,  or  pontal,  olives  there  is  a  system  of  fibers 
which  envelops  and  covers  the  olivary  nuclei  to  decussate  upon  the 
median  line  back  of  the  pyramids.  It  is  to  this  system  of  fibers 
which  unite  the  nuclei  of  the  auditory  nerves  and  the  olives  that 
Edinger  has  given  the  name  of  trapezoid  body. 

The  longitudinal  fibers  are  in  three  groups:  1.  The  anterior 
bundle,  which  contains  the  middle  fibers  of  the  cerebral  peduncle. 
It  is  continuous  with  the  superficial  motor  fibers  of  the  anterior 
pyramids  of  the  medulla;  farther  down  it  is  still  in  connection  with 
the  pyramidal  column  of  the  opposite  side  of  the  spinal  cord. 

2v  The  middle  column,  or  fillet. 

3.  The  third  group,  the  posterior  longitudinal  column,  passes 
along  the  floor  of  the  fourth  ventricle,  from  which  it  is  separated  by 
a  plane  of  transverse  fibers.  It  is  continuous  with  the  anterior 
column  of  the  cord  to  form,  consequently,  the  longitudinal  com- 
missural  column.  Some  of  the  fibers  of  this  bundle  decussate  with 
their  fellows  of  the  opposite  side  to  unite  among  themselves  the 
nuclei  of  the  motor  nerves  of  the  eye  and  the  gray  mass  of  the 
4 aqueduct  of  Sylvius. 

Each  bundle  is  separated  from  its  fellow  by  a  plane  of  trans- 
verse fibers :  the  strata  zonale  and  profundum. 

The  gray  substance  of  the  pons  is  found  isolated  in  small  islands 
(nuclei  of  the  pons),  which  are  located  between  the  various  white 
layers  which  have  just  been  mentioned. 

One  of  these  nuclei,  the  most  voluminous  of  all,  is  situated  near 
the  median  raphe  at  the  site  of  the  junction  of  the  inferior  and 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          431 

middle  thirds  of  the  pons.  It  bears  the  name  of  reticulated  nucleus 
of  the  pons.  At  a  slightly  higher  level  is  found  another,  known  as 
the  central  nucleus.  To  these  two  nuclei  are  joined  the  root-bundles 
of  the  antero-lateral  column  of  the  cord. 

In  addition,  as  a  continuation  of  the  posterior  horns  of  the  cord, 
there  exists  a  nucleus  which  gives  origin  to  the  trigeminus.  Inward 
and  somewhat  to  the  front  is  found  a  gray  mass  composed  of  large 
multipolar  cells.  These  represent  the  caput  of  the  anterior  horn. 
It  forms  the  nucleus  of  origin  of  the  motor  root  of  the  trigeminus. 

Upon  each  side  of  the  raphe  and  very  close  to  the  surface  of  the 
floor  of  the  fourth  ventricle  are  found  other  gray  nuclei,  as  of  the 
facial  and  oculomotor;  also  a  yellow  mass  of  an  S-shape  which  forms 
the  superior  olive  of  the  pons.  This  latter  is  connected  with  the 
auditory  apparatus.  The  gray  substance  of  the  medulla  is  prolonged 
into  the  pons  to  form  the  origin  of  the  cranial  nerves. 

CEREBRAL  PEDUNCLES. 

The  peduncles  of  the  brain  are  two  white  cords  which  extend 
from  the  superior  face  of  the  pons  in  a  divergent  manner  up  in  the 
optic  thalami.  They  are  somewhat  flattened  from  top  to  base.  Their 
volume  is  in  direct  relation  to  that  of  the  brain.  The  peduncles 
are  much  larger  than  the  columns  of  the  cord  reunited;  they  con- 
tain fibers  coming  from  the  gray  matter  of  the  medulla,  pons,  corpora 
quadrigemina,  locus  niger,  and  masses  of  gray  matter  lying  in  a  line 
along  the  aqueduct  of  Sylvius.  In  length  the  peduncles  measure 
about  three-fourths  of  an  inch. 

Immediately  after  their  emergence  from  the  pons  they  separate, 
each  one  making  its  way  toward  its  corresponding  hemisphere  of 
the  cerebrum.  Between  them  there  remains  a  triangular  space,  the 
inter  peduncular  space,  filled  in  its  back  part  by  a  cribiform  white 
layer  containing  a  great  number  of  vascular  openings.  The  latter 
is  known  as  the  posterior  perforated  space.  This  space,  bounded  in 
front  by  the  optic  chiasm,  is  occupied  by  the  mammillary  eminences 
and  tuber  cinereum. 

Texture  of  the  Peduncles. — A  transverse  section  of  the  cerebral 
peduncles  gives  an  idea  of  the  architecture  of  the  large  nerve-trunks. 
In  a  cut  of  this  kind  it  is  seen  that  the  peduncles  are  separated  into 
two  white,  superposed  layers  by  a  black  line :  the  locus  niger. 

The  inferior  level,  or  crusta,  of  the  peduncle  is  formed  in  great 
part  by  a  large,  flat,  white  bundle  which  is  a  prolongation  of  the 
motor  fibers  extending  to  the  spinal  cord.  The  crusta  extends  from 


432  PHYSIOLOGY. 

the  internal  capsule  through  the  pons  to  the  ventral  portion  of  the 
medulla  oblongata.  From  the  internal  capsule  its  fibers  become  lost 
in  the  cortical  layer  of  the  hemisphere  of  its  own  side.  The  crusta 
is  composed  of  two  bundles,  the  internal,  or  cortico-pontal,  and  the 
external,  or  voluntary  motor,  bundle.  The  cortico-pontal  bundle  acts 
as  a  commissure  between  the  cerebrum  and  cerebellum.  It  passes 
from  the  anterior  region  of  the  cerebrum  through  the  peduncles  to 
the  pons  and  medulla,  to  end  in  the  cerebellum.  The  voluntary  motor 
bundle  descends  from  the  motor  regions  of  the  cortex  to  end  in  the 
nuclei  of  origin  of  the  cranial  and  spinal  nerves. 

TEGMENTUM. — The  superior  layer  of  the  cerebral  peduncle, 
known  as  the  tegmentum,  consists  of  masses  of  gray  matter  and 
fibers  which  extend  through  the  posterior  end  of  the  medulla  ob- 
longata, pons,  and  crura  up  to  the  optic  thalami.  At  the  height  of 
the  corpora  quadrigemina  is  a  reddish  column  formed  of  multipolar 
cells.  It  is  the  red  nucleus  of  the  tegmentum.  In  the  tegmentum, 
between  the  fillet  and  the  red  nucleus,  is  found  the  formatio  reticu- 
laris. 

THE  Locus  NIGER,  which  separates  the  pes,  or  crusta,  from  the 
tegmentum,  consists  of  highly  pigmented  cells.  They  are  like  the  cells 
of  the  motor  regions  of  the  cortex.  Thus,  the  locus  niger  might  be 
considered  as  a  sort  of  motor  ganglion  whose  cells  are  charged  with 
black  pigment. 

THE  FOURTH  VENTRICLE. 

The  fourth  ventricle  is  a  rhomboid  cavity  (sinus  rhomboidalis) 
imbedded  upon  the  posterior  surface  of  the  medulla  oblongata  and 
pons.  It  is  the  space  into  which  the  central  canal  of  the  cord  opens 
superiorly.  It  is  flattened  from  top  to  base;  and  has  an  inferior 
wall,  or  floor;  a  superior  wall,  or  vault;  and  four  angles. 

Floor  of  the  Ventricle. — The  floor  of  the  fourth  ventricle  is 
lozenge-shaped,  being  formed  by  two  triangles  placed  in  contiguity 
at  their  bases.  It  is  lined  by  a  layer  of  gray  matter,  which  is  but  a 
continuation  of  that  of  the  cord. 

The  inferior  triangle  (calamus  scriptorius)  belongs  to  the  pos- 
terior face  of  the  medulla;  the  superior  triangle  to  the  posterior 
face  of  the  pons. 

Upon  the  median  line  of  the  floor  there  is  a  slight  groove :  the 
handle  of  the  calamus.  On  each  side  of  this  groove  the  surface  of 
the  floor  presents  small,  rounded,  and  elongated  prominences.  These 
have  been  described  at  some  length  previously,  so  that  now  they  will 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          433 

be  but  mentioned.  In  the  inferior  triangle,  from  the  handle  of  the 
calamus  to  the  restiform  body,  they  are:  (1)  trigonum  Jiypoglossi; 
(2)  ala  cinerea,  or  trigonum  vagi;  (3)  trigonum  acustici. 

In  the  superior  triangle,  upon  each  side  of  the  median  groove 
and  near  the  base  of  the  triangle,  are  seen  two  rounded  eminences: 
(1)  eminentia  teres  and  (2)  the  locus  cceruleus. 

The  various  eminences  correspond  to  the  origin  of  the  cranial 
nerves.  Thus,  in  the  locus  coeruleus  is  located  the  origin  of  the 
small  root  of  the  trigeminus ;  in  the  teres  eminentia  the  common  ori- 
gin of  the  facial  and  oculomotor;  in  the  trigonum  hypoglossi  is  the 
origin  of  the  hypoglossal  nerve ;  in  the  ala  cinerea,  or  trigonum  vagi, 
occurs  the  origin  of  the  motor  roots  of  the  glosso-pharyngeal  nerves, 
pneumogastric,  and  spinal  accessory;  in  the  trigonum  acustici  are 
found  the  fibers  of  the  auditory  and  the  sensory  fibers  of  the  mixed 
nerves,  glosso-pharyngeal,  vagus,  and  spinal  accessory.  The  trigo- 
num hypoglossi  corresponds  to  the  funiculus  teres;  the  ala  cinerea  to 
a  depression :  posterior  fovea. 

At  the  level  of  the  middle  of  the  floor  of  the  fourth  ventricle  a 
variable  number  of  striae  go  out  from  the  median  groove  toward  the 
]ateral  angles.  Here  they  converge  somewhat  and  form,  according 
to  some  authors,  the  posterior  root  of  the  auditory  nerve.  The 
striations  constitute  the  larbce  of  the  calamus. 

The  gray  matter  of  the  spinal  cord,  when  it  penetrates  into  the 
medulla,  exposes  itself  upon  the  floor  of  the  fourth  ventricle.  The 
horns  of  the  central  gray  column  of  the  cord  are  found  broken  up 
into  many  parts  by  the  decussation  of  the  pyramids  and  fillet.  By 
reason  of  this,  the  gray  matter  in  the  floor  of  the  ventricle  repre- 
sents four  irregular,  discontinuous  longitudinal  columns;  two  are 
central,  with  a  superficial  one  on  each  side.  These  columns  are  pro- 
duced by  the  bases  and  detached  heads  of  the  anterior  and  posterior 
horns  of  the  central  gray  column.  From  the  anterior  gray  matter 
proceed  motor  cranial  nerves;  from  the  posterior  gray  matter  spring 
sensory  cranial  nerves. 

The  lateral  boundaries  of  the  ventricle  are,  in  the  lower  half,  the 
clavse  of  the  funiculi  graciles,  the  cuneati,  and  the  restiform  bodies. 
In  its  upper  half  the  superior  peduncles  of  the  cerebellum  form  the 
limits. 

AQUEDUCT  OF  SYLVIUS. 

The  aqueduct  of  Sylvius  is  a  canal  a  centimeter  and  a  half  long. 
It  is  hollowed  out  beneath  the  corpora  quadrigemina.  By  means  of 


434 


PHYSIOLOGY. 


this  aqueduct  the  fourth  ventricle  communicates  with  the  third.  It 
is  derived  from  the  middle  cerebral  vesicle.  Its  walls  are  formed 
above  by  the  valve  of  Vieussens,  the  corpora  quadrigemina,  and  the 
white,  posterior  commissure.  Its  base,  or  floor,  is  formed  by  the 
tegmentum.  Its  floor  is  grooved  by  the  continuation  of  the  median 
groove  of  the  fourth  ventricle.  Its  walls  are  composed  of  gray 
matter  continued  from  the  spinal  cord. 


rdacb 


Fig.  105.— The  Fillet,  Ending  Chiefly  in  the  Ventral  Nucleus  of  the  Optic 

Thalamus  and  then  United  by  New  Neuraxons  (Upper 

Fillet)  to  Parietal  Cortex. 

FILLETS. 

The  chief  fillet  consists  of  the  axis-cylinders  from  GolPs  and 
Burdach^s  nuclei,  which  decussate  under  the  floor  of  the  fourth 
ventricle,  then  pass  up  through  the  tegmentum,  and  chiefly  end  in 
the  ventral  nucleus  of  the  optic  thalamus.  From  new  neuraxons  it 
goes  through  the  posterior  part  of  the  internal  capsule  to  the  ascend- 
ing frontal  and  ascending  parietal  convolutions.  It  is  a  continuation 
of  the  sensory  tract. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          435 

The  lateral  fillet  also  starts  from  the  nuclei  of  Goll  and  Burdach 
and  is  chiefly  composed  of  axis-cylinders  from  the  end  nuclei  of  the 
auditory  nuclei  and  the  superior  olivary  body;  it  then  passes  into 
the  posterior  corpora  quadrigemina,  and  thence  by  means  of  the 
brachium  posterioris  of  the  corpora  quadrigemina  through  the  pos- 
terior limb  of  the  internal  capsule  to  the  first  and  second  temporal 
convolutions.  It  is  made  up  mainly  of  auditory  fibers. 

THE   BRAIN. 

The  weight  of  the  brain  is  about  fifty  ounces.  However,  the 
weight  of  the  brain  may  be,  as  in  the  case  of  Couvier,  sixty-five 
ounces.  It  is  greater  in  civilized  persons  than  in  savage  tribes;  it  is 
likewise  greater  in  the  male  than  in  the  female;  in  an  eminent  man 
than  in  an  ordinary  man.  But  what  really  shows  the  superiority  of  the 
brain  is  not  so  much  its  size  nor  the  exuberance  of  its  convolutions, 
but  the  well-balanced  development,  the  harmony,  of  all  of  its  parts. 

External  Form. — The  brain  is  composed  of  two  symmetrical 
halves,  or  hemispheres.  These  are  nearly  entirely  separated  from  one 
another  by  the  great  longitudinal  fissure.  The  parts  which  are  intact 
are  located  at  the  center  and  base  and  comprise  the  corpus  callosum 
and  floor  of  the  fourth  ventricle.  The  surfaces  of  the  hemispheres  are 
separated  into  lobes  and  convolutions  by  various  fissures.  The  con- 
volutions appear  to  be  infoldings  of  the  gray  matter  of  the  brain 
within  its  rigid  confines,  the  cranial  vault.  The  mode  of  spreading 
of  the  fibers  of  the  peduncle  may  have  something  to  do  with  their 
conformation  also.  The  end  obtained  by  their  presence  is  to  lodge  a 
much  larger  gray  mass  within  a  given  space. 

There  are  five  principal  fissures  in  the  brain:  (1)  the  great  longi- 
tudinal; (2)  the  great  transverse  fissure  between  the  cerebrum  and 
cerebellum;  (3)  the  fissure  of  Sylvius;  (4)  fissure  of  Rolando;  (5) 
.  parieto-occipital  fissure. 

As  previously  stated,  the  great  longitudinal  fissure  runs  antero- 
posteriorly  to  separate  the  two  hemispheres  of  the  brain. 

At  its  posterior  end  and  at  right  angles  to  it  lies  the  great 
transverse  fissure.  By  it  the  posterior  portion  of  the  cerebrum  is 
separated  from  the  cerebellum. 

The  fissure  of  Sylvius  begins  at  the  base  of  the  brain  at  the 
anterior  perforated  space.  It  passes  outward  to  the  external  sur- 
face of  the  hemispheres,  where  it  divides  into  two  branches.  The 
one  branch  passes  upward  (ascending  limb) ;  the  other,  a  larger  one, 
runs  nearly  horizontally  backward  (horizontal  limb). 


436  PHYSIOLOGY. 

The  fissure  of  Eolando  commences  at  the  great  longitudinal 
fissure,  half  an  inch  behind  its  middle,  measuring  from  the  glabella 
to  the  external  occipital  protuberance.  It  runs  down  and  forward  to 
terminate  a  little  above  the  horizontal  limb  of  the  fissure  of  Sylvius. 

The  parieto-occipital  fissure  commences  about  midway  between 
the  posterior  extremity  of  the  brain  and  the  fissure  of  Eolando  to 
run  down  and  forward  for  a  variable  distance. 

The  fissures  which  have  just  been  mentioned  are  made  use  of  to 
map  out  the  surface  of  the  hemispheres  into  regions  to  which  the 
term  lobes  has  been  applied.  This  mapping  is  purely  artificial  and 
has  no  clinical  or  pathological  bearing;  in  many  instances  the  lines 
dividing  the  lobes  are  purely  imaginary.  However,  anatomists  are 
accustomed  to  speak  of  six  lobes:  (1)  frontal;  (2)  parietal;  (3) 
occipital;  (4)  temporal;  (5)  limbic,  and  (6)  island  of  Reil. 

The  island  of  Reil,  or  central  lobe,  is  located  at  the  bottom  of 
the  fissure  of  Sylvius.  It  is  a  portion  of  the  cerebral  cortex  which 
is  overhung  by  the  operculum. 

The  convolution  of  Broca  is  that  portion  of  the  inferior  frontal 
convolution  which  winds  around  the  ends  of  the  anterior  and  ascending 
limbs  of  the  fissure  of  Sylvius.  It  is  characteristic  in  that  it  is  the 
speech-center  and  also  that  it  is  better  developed  upon  the  left  side 
in  right-handed  people. 

On  the  internal,  or  mesial,  aspect  of  the  hemispheres  are  the 
following  fissures  and  convolutions:  The  convolution  immediately 
bounding  the  corpus  callosum  is  termed  the  gyrus  fornicatus;  the 
hippocampal  gyrus  ends  inferiorly  in  a  crochetlike  extremity,  termed 
the  uncus.  The  gyri  fornicatus  and  hippocampus  together  form  the 
great  limbic  lobe;  the  marginal  convolution  is  merely  the  internal 
aspect  of  the  convolutions  of  the  frontal  and  parietal  lobes.  That 
portion  which  forms  the  mesial  aspect  of  the  ascending  frontal  con- 
volution is  known  as  the  paracentral  lobule.  Upon  the  mesial 
aspect  of  the  postero-parietal  lobule  is  a  quadrilateral  lobule:  the 
prascuneus. 

Between  the  parieto-occipital  and  calcarine  fissures  is  a  wedge- 
shaped  lobule  called  the  cuneus. 

Structure  of  the  Cerebral  Convolutions. — The  gray  matter  of  the 
cerebral  cortex  has  been  divided  into  four  layers : — 

1.  The  superficial  layer. 

2.  The  layer  of  small  pyramidal  cells. 

3.  The  layer  of  large  pyramidal  cells. 

4.  The  layer  of  polymorphous  cells. 


Fig.  106. — Section  through  the  Cerebral  Cortex  of  a  Mammal. 
(EDINGER  and  CAJAL.) 

1,  Superficial,  or  molecular,  layer.  2,  Layer  of  small  pyramidal  cells.  3,  Layer  of 
large  pyramidal  cells.  4,  Layer  of  polymorphous  cells,  a,  6,  c,  Ganglionic  cells,  d, 
Fusiform  cells,  e,  Fibers,  f,  Pyramidal  cells,  (j,  Multipolar  cells. 


438  PHYSIOLOGY. 

The  first  layer  contains  the  cells  of  Cajal.  In  this  layer  termi- 
nate many  of  the  fibers  coming  from'  the  spinal  cord,  medulla,  and 
cerebellum. 

The  second  layer  contains  the  small  pyramidal  cells,  whose 
axons  run  into  the  superficial  layer. 

The  third  layer  contains  the  cells  of  Martinotti,  with  the  large 
pyramidal  cells. 

The  fourth  layer  is  made  up  of  triangular,  small  pyramidal,  and 
spindle  cells. 

The  white  matter  of  the  hemispheres  consists  of  medullated 
fibers  whose  size  is  varied.  As  a  rule,  however,  they  are  smaller  than 
those  of  the  cord  and  bulb.  For  the  most  part,  they  are  arranged  in 
bundles  separated  by  layers  of  neuroglia. 

Central  Ganglia  of  the  Brain. — At  the  level  of  the  hilus  of  the 
brain  the  cerebral  peduncles  sink  into  the  body  of  the  two  hemi- 
spheres. They  contain  fibers  which  proceed  from  the  cord,  pons, 
and  cerebrum  to  the  brain,  as  well  as  those  fibers  from  the  brain  to 
the  cord,  pons,  and  cerebellum.  There  are  also  direct  fibers  which 
reach  from  the  peduncles  to  the  brain  cortex.  However,  there  are 
other  indirect  or  ganglionic  fibers  which  communicate  previously  in 
the  nuclei  or  ganglia  of  the  gray  substance.  The  ganglia  referred  to 
are :  the  optic  thalami  and  the  corpora  striata.  The  optic  thalami  are 
two  oval  bodies  placed  upon  the  tract  of  the  cerebral  peduncles.  At 
the  posterior  part  of  the  thalamus  are  the  external  and  internal 
geniculate  bodies.  Between  the  pulvinar  and  origin  of  the  pineal 
gland  is  found  a  small  surface,  slightly  depressed  and  of  triangular 
form;  it  is  the  triangle  of  the  habenula.  Within  this  triangle  is  a 
small  prominence  known  as  the  nucleus  of  the  habenula.  The  haben- 
ula  is  the  peduncle  of  the  pineal  gland. 

The  inferior  surface  of  the  thalamus  rests  upon  the  cerebral 
peduncle,  from  which  it  receives  some  fibers.  In  the  rear  it  remains 
free,  and  presents  two  nipplelike  swellings:  the  geniculate  bodies. 
One  lies  internal;  the  other  external. 

Monakow  divides  the  nuclei  of  the  thalamus  as  follows :  (1)  an- 
terior, (2)  median,  (3)  ventral,  (4)  posterior,  and  (5)  pulvinar.  The 
posterior  root-fibers  arborize  about  the  nuclei  of  Goll  and  Burdach. 
From  there  they  are  continued  by  a  second  neuraxon  to  end  in  the 
ventral  nucleus  of  the  thalamus.  Each  thalamus  has  a  double  con- 
nection with  all  parts  of  the  cerebral  cortex  by  neuraxons  from  its 
various  nuclei  to  the  cortex,  and  by  neuraxons  from  the  pyramidal 
cells  of  all  parts  of  the  cortex.  The  neuraxons  of  the  ganglionic 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          439 

cell-layer  of  the  retina  end  about  the  cells  of  the  pnlvinar  and  ex- 
ternal geniculate  body,  thus  connecting  it  with  the  primary  division 
of  the  optic  tract.  It  has  also  a  double  connection  with  the  occipital 
lobes  by  neuraxons  from  the  pulvinar  cells  (optic  radiations),  which 
terminate  in  the  pyramidal  cells  of  the  occipital  cortex  and  by  neiir 
raxons  from  the  pyramidal  cells  of  that  lobe  which  end  in  the  cells 
of  the  pulvinar. 

Corpora  Striata. — The  corpora  exist  as  two  large  ovoid  gray 
masses  lodged  within  the  thickness  of  the  frontal  lobe.  They  are 
situated  in  front  of  and  slightly  outward  from  the  optic  thalami. 
The  outer  surfaces  of  the  corpora  are  in  relation  with  the  island  of 
Eeil  and  the  centrum  ovale  of  the  hemispheres.  Internally,  they 
are  in  apposition  with  the  optic  thalami  and  the  gray  layer  of  the 
third  ventricle.  They  are  formed  of  two  large  nuclei:  the  caudate 
and  lenticular. 

The  nucleus  caudatus  is  so  named  from  its  resemblance  to  a  pear 
in  shape.  It  lies  inside  the  lateral  ventricle  upon  its  floor.  The 
cells  of  this  nucleus  are  of  two  types — sensory  and  motor;  the  cells 
of  the  motor  type  seem  to  be  more  abundant. 

The  nucleus  lenticularis,  a  part  of  the  corpus  striatum,  is  sepa- 
rated from  the  caudate  nucleus  by  the  internal  capsule.  By  reason 
of  its  situation  near  the  center  of  the  body  of  the  hemisphere  and 
outside  of  the  ventricle  it  is  called  the  extraventricular  nucleus  of 
the  corpus  striatum. 

The  lenticular  nucleus  is  divided  into  three  segments  by  two 
layers  of  white  matter  placed  within  its  thickness.  The  segments 
are  distinguished  from  one  another  by  their  color,  which  is  most 
pronounced  in  the  external  segment.  The  latter  has  received  the 
name  of  putamen.  The  two  other  segments  are  known  as  the  in- 
ternal and  external  segments  of  the  globus  pallidus. 

Hence  it  ensues  that  the  corpus  striatum  has  the  general  char- 
acter of  the  letter  c,  its  upper  extremity,  or  branch,  being  repre- 
sented by  the  caudate  nucleus;  its  lower  branch  by  the  lenticular 
nucleus.  The  point  of  union  of  the  two  forms  the  knee.  The 
corpora  striata  are  of  cortical  origin,  and  not  of  central  origin,  as  is 
the  thalamus.  That  is  to  say,  the  nerve-impulses  of  voluntary  move- 
ment ordered  by  the  cortex  descend  to  the  corpora  striata,  where 
they  undergo  transformation  before  appearing  as  muscular  move- 
ments. 

The  Claustrum. — To  the  corpora  striata  is  attached  a  thin  layer 
of  gray  substance,  so  placed  that  it  occupies  the  field  between  the 


440  PHYSIOLOGY. 

lenticular  nucleus  and  the  island  of  Reil.  This  band,  derived  from 
the  cortex  in  a  manner  similar  to  those  fibers  of  the  corpora  striata 
just  mentioned,  is  the  claustrum.  It  is  separated  from  the  external 
surface  of  the  lenticular  nucleus  by  a  band  of  white  substance :  the 
external  capsule. 

The  claustrum  is  composed  of  spindle  cells,  quite  like  those 
found  in  the  deep  layer  of  the  cortex.  The  claustrum  should  be  con- 
sidered as  a  part  of  the  cortex  that  has  been  detached  by  reason  of 
the  passage  of  a  bundle  of  fibers  of  association.  These  fibers  unite 
the  various  convolutions  among  themselves. 

The  corpora  quadrigemina  are  four  small  bodies  or  rounded  emi- 
nences. .They  are  composed,  for  the  greater  part,  of  gray  matter, 
although  covered  externally  by  and  containing  in  their  interior  some 
white  fibers.  They  lie  beneath  the  pulvinar  of  the  optic  thalamus. 

The  corpora  are  arranged  in  two  pairs:  one  anterior,  the  other 
posterior. 

The  upper,  or  anterior,  pair  is  broader,  longer,  and  darker  than 
the  posterior  pair.  Laterally  the  corpora  extend  into  distinct  and 
prominent  tracts  of  white  substance. 

The  lower,  or  posterior,  corpora  are  composed  almost  entirely  of 
gray  matter. 

Internal  Capsule. — The  name  of  internal  capsule  is  given  to  a 
thick  band  of  white  fibers  situated  between  the  optic  thalamus  and 
caudate  nucleus  on  one  side  and  the  lenticular  nucleus  on  the  other. 
In  a  frontal  section  of  the  brain  the  tract  is  seen  to  follow  a  course 
upward  and  outward  in  an  oblique  manner  between  the  preceding 
nuclei.  Downward  it  is  continuous  with  the  cerebral  peduncle. 

Where  the  capsule  enters  the  lenticular-striate  defile  it  expands 
like  a  bundle  of  stalks  to  form  the  corona  radiata  of  Eeil. 

If  studied  horizontally,  the  internal  capsule  is  seen  to  present 
the  shape  of  an  angle  opening  outward  and  embracing  the  lenticular 
nucleus.  The  capsule  seems  to  be  composed  of  two  parts  or  segments 
and  a  bend,  or  genu. 

The  anterior  segment  is  placed  between  the  lenticular  and 
caudate  nuclei;  it  bears  the  name  of  arm,  or  lenticulo-striate  segment. 
The  posterior  segment,  situated  between  the  optic  thalamus  and 
lenticular  nucleus,  for  this  reason  takes  the  name  of  lenticulo -optic 
segment. 

The  point  of  union  of  the  two  segments  is  called  the  knee,  or 
genu.  Its  position  is  exactly  at  the  center  of  the  three  nuclei  just 
mentioned. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  441 

CAPSULAR  STRUCTURE. — With  the  naked  eye  or  even  a  microscope 
the  internal  capsule  presents  itself  as  a  homogeneous  structure, 
composed  of  white  fibers.  There  is  nothing  in  its  appearance  to  let 
anyone  suppose  that  there  are  different  tracts  or  bundles.  How- 
ever, pathological  anatomy,  with  its  secondary  degeneration,  and 
embryology,  by  reason  of  the  myelin  appearing  in  the  bundles  at 
different  stages  of  development  of  the  foetus,  reveal  a  number  of 
segments  perfectly  separated  either  from  a  functional  or  pathological 
point  of  view. 

The  three  bundles  of  fibers  are  distributed  somewhat  as  follows 
in  the  capsule: — 

1.  The  Cortico-Pontal-Cerebellar  Tract  is  composed  of  neuraxons 
coming  from  the  pyramidal  cells  of  the  frontal  lobes.    Then  the  neu- 
raxons pass  through  the  anterior  two-thirds  of  the  anterior  segment 
of  the  internal  capsule,  then  through  the  crusta,  ending  in  some  of 
the  pontal  nuclei.     These  pontal  nuclei  are  joined  by  neuraxons  to  the 
fibers  chiefly  from  half  of  the  cerebellum  of  the  opposite  side,  al- 
though some  fibers  are  from  the  cerebellar  half  of  the  same  side. 
Hence  the  frontal  lobes  are  anatomically  connected  with  the  oppo- 
site cerebellar  hemisphere. 

2.  The  Motor  Tract,  which  arises  from  the  neuraxons  of  the 
large  pyramidal  cells  of  the  ascending  parietal  and  ascending  frontal 
convolutions  and  paracentral  convolutions;    then  go  through  the  an- 
terior two-thirds  of  the  posterior  segment  of  the  internal  capsule; 
then  through  the  crusta  to  the  anterior  pyramids  of  the  medulla 
oblongata,    where    they    partly    decussate,    becoming    the    crossed 
pyramidal  tract  of  the  opposite  side  of  the  spinal  cord,  ending  in  the 
cells  of  the  anterior  horns.     Part  of  the  motor  tract  passes  down  on 
the  side  upon  which  it  originated  as  the  tract  of  Tiirck,  then  through 
the  anterior  white  commissure  into  the  cells  of  the  anterior  horn 
of  the  opposite  side  of  the  cord.    Here  we  have  a  long  neuraxon  or 
axon  from  the  motor  convolution  to  the  anterior  horns  of  the  oppo- 
site side  of  the  spinal  cord.    From  here  a  second  axoii  starts  out  to 
supply  the  muscles,  making  only  two  axons  in  the  motor  tract. 

The  motor  tract  includes  a  band  of  fibers  running  from  the 
cortex  to  the  nucleus  of  the  various  motor  cranial  nerves.  Thus  the 
cortex  sends  motor  fibers  to  the  nucleus  of  the  third,  fourth,  motor 
division  of  fifth,  the  sixth,  the  seventh,  the  motor  divisions  of  the 
ninth  and  tenth,  and  the  eleventh  and  twelfth  pairs.  We  only  know 
the  cortical  origin  of  the  seventh,  the  motor  branch  of  the  fifth,  and 
the  hypoglossal,  and  these  originate  from  the  lowest  third  of  the 


442  PHYSIOLOGY. 

ascending  frontal  and  ascending  parietal  convolutions;  then  they 
pass  through  the  knee,  or  genu,  of  the  internal  capsule  and  continue 
through  the  crusta  until  they  end  in  the  nuclei  of  the  various  cranial 
motor  nerves.  As  this  tract  passes  through  the  genu  of  the  capsule 
it  is  known  as  the  geniculate  tract :  a  part  of  the  main  motor  tract. 

3.  The  Sensory  Tract. — Its  axons  arise  in  the  ganglion  of  the 
posterior  root  and  extend  from  the  skin  and  muscles  to  the  spinal 
cord,  where  they  divide  into  an  ascending  and  descending  branch. 
The  descending  branches  arborize  about  the  cells  in  the  gray  matter 
of  the  cord.  The  ascending  branches  in  great  part  ascend  in  the 
columns  of  Goll  and  Burdach  and  arborize  in  the  cells  of  the  nuclei 
of  Goll  and  Burdach.  From  the  nuclei  of  Goll  and  Burdach  a  second 
series  of  axons  pass  under  the  name  of  the  fillet  or  lemniscus  or  inter- 
olivary  tract,  decussating  under  the  floor  of  the  fourth  ventricle  and 
chiefly  arborize  about  the  cells  of  the  ventral  nucleus  of  the  thalamus. 
From  the  ventral  nucleus  a  third  set  of  neuraxoiis  arise  and  go 
through  the  posterior  part  of  the  posterior  segment  of  the  internal 
capsule  to  the  ascending  frontal  and  ascending  parietal  convolutions. 
This  tract  also  receives  the  neuraxons  of  the  sensory  nuclei  of  the 
cranial  nerves  running  to  the  cortex  excepting  the  auditory  nucleus. 
In  the  internal  capsule  the  motor  fibers  going  to  the  face  are  in 
front;  next  the  arm-  and  then  the  leg-  fibers.  Hence  lesions  occur- 
ring in  the  anterior  two-thirds  of  the  posterior  limb  of  the  capsule 
cause  motor  troubles;  lesions  in  the  posterior  third  cause  sensory 
troubles.  The  sensory  tract  is  composed  of  three  neuraxoiis:  one 
from  the  skin  to  GolPs  and  Burdaclr's  nuclei,  the  second  from  these 
nuclei  to  the  ventral  nucleus  of  the  thalamus,  and  the  third  from  this 
ventral  nucleus  to  the  cortex.  Pain  and  temperature  sensations 
travel  through  the  gray  matter. 

Blood-supply  of  the  Brain. — The  brain  is  freely  supplied  with 
arteries.  The  brain  with  its  enveloping  membrane  is  said  to  receive 
fully  one-fifth  of  the  entire  quantity  of  blood  within  the  body. 

The  brain  with  its  adnexa  is  supplied  by  the  two  vertebrals  and 
the  two  internal  carotids,  with  their  numerous  branches.  These 
principal  vessels  form  a  free  anastomosis  at  the  base  of  the  brain, 
known  as  the  circle  of  Willis.  The  circle  is  composed  of  the  tip  of 
the  basilar,  the  two  posterior  cerebrals,  the  two  posterior  communi- 
cating, the  tips  of  the  two  internal  carotids,  the  two  anterior  cere- 
brals, and  the  anterior  communicating,  which  connects  the  two 
anterior  cerebrals. 

The  nucleus  caudatus  and  the  nucleus  lenticularis  are  almost 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          443 

exclusively  supplied  by  the  middle  cerebral  artery,  whose  branches 
pass  through  the  foramina  of  the  anterior  perforated  space.  The 
branches  are  subdivided  into  the  lenticular,  lenticulo-striate,  and 
lenticulo-thalamic  arteries.  These  vessels  pass  to  their  terminations 
without  anastomosing  with  one  another.  One  of  the  lenticulo-striate 
arteries  which  passes  through  the  outer  part  of  the  putamen  is  very 
frequently  the  seat  of  haemorrhage.  By  Charcot  it  was  named  the 
artery  of  cerebral  haemorrhage. 

The  lymph  finds  its  way  out  of  the  various  areas  of  the  brain  by 
means  of  perivascular  spaces  in  the  tunica  adventitia  of  the  blood- 
vessels. These  spaces  communicate  with  the  subarachnoid  space  at 
the  surface  of  the  brain. 

\ 
PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM.1 

Comparison  of  Nerve  and  Muscle. — In  the  study  of  the  general 
physiology  of  muscle  there  was  first  analyzed  its  most  apparent  phe- 
nomenon: muscular  contraction.  Then  was  considered  the  forces 
which  provoke  muscular  contraction,  with  modifications  of  muscular 
excitability. 

Practically  the  same  course  will  be  adopted  in  treating  of  the 
general  physiology  of  the  nerves.  First  there  will  be  considered  that 
property  comparable  to  the  muscular  contraction ;  in  turn  will  follow 
a  study  of  the  forces  which  produce  the  nerve-wave,  with  modifications 
also  of  the  nervous  excitability. 

Thus,  there  will  be  established  a  sort  of  parallel  between  nerv- 
ous and  muscular  functions;  .muscular  contraction  and  nerve-wave; 
muscular  irritability  and  nervous  irritability;  muscular  excitability 
and  nervous  excitability. 

When  a  nerve  is  separated  from  its  nervous  centers  and  no  force 
intervenes  to  modify  its  state,  then  it  will  remain  inert.  There  will 
be  neither  movement  nor  sensibility.  Neither  will  the  nerve  come 
into  action  unless  it  be  stimulated  or  excited. 

Nerve  Excitability. — When  a  stimulus  is  applied  to  a  nerve  it 
enters  into  activity.  There  are  various  ways  in  which  this  activity 
is  manifested,  as  by  modification  of  motion  or  sensation,  and  besides 
these  external  manifestations  a  latent  property  in  the  nerve  itself, 
known  as  negative  variation,  which  it  undergoes  during  activity. 
The  most  striking  exhibit  of  nerve  activity  is  the  contraction  of  the 
muscle  supplied  by  the  nerve.  If  we  would  estimate  the  irritability 


1  For  anatomy  of  the  cerebellum  and  mesencephalon  see  subsequent  pages. 


444  PHYSIOLOGY. 

of  a  nerve  it  is  necessary  to  know  accurately  both  the  intensity  of 
the  stimulus  and  the  result  produced.  Irritability  requires  for  its 
due  manifestation  the  integrity  of  the  nerve  and  an  unimpaired  cir- 
culation and  nutrition.  But  even  in  a  normal  state  the  irritability  of 
the  nerve  is  extremely  variable  and  in  a  constant  state  of  instability. 

Intervals  of  repose  alternating  with  activity  are  the  most  favor- 
able conditions  for  the  maintenance  of  irritability.  When  a  nerve 
remains  at  rest  for  a  long  time  the  irritability  diminishes  and  may 
even  be  abrogated,  conducing  to  degeneration  of  the  nerve.  Ex- 
cessive stimulation  has  a  similar  tendency  to  destroy  the  nerve. 

For  a  proper  appreciation  of  so  delicate  a  structure  as  the 
nervous  tissue  and  the  changes  of  a  fundamental  order  occurring 
within  it,  the  student  should  picture  to  himself  the  physical  condi- 
tion of  the  nerve ;  how  it  is  composed  of  molecules  in  a  state  of  stable 
equilibrium.  With  this  conception  he  will  readily  see  how  any  ex- 
ternal stimulus  may  produce  molecular  movement  in  one  direction 
and  hold  them  in  said  position  for  any  variable  time. 

With  cessation  of  the  exciting  cause  the  molecules  will  be  re- 
leased from  their  rigid  condition  and  immediately  return  to  their 
previous  normal  state.  This  "return"  is  the  occasion  of  changes 
in  the  opposite  direction.  Thus,  any  power  that  is  capable  of  pro- 
ducing movement  in  any  one  direction  is  sure  to  be  succeeded  by 
movement  in  the  opposite  direction  as  the  molecules  of  the  nerve 
resume  their  normal,  stable  equilibrium. 

This  fundamental  principle  must  constantly  be  kept  before  the 
student's  mind,  since  many  of  the  physiological  phenomena  of  the 
nervous  system  are  dependent  upon  it,  or  their  conception  is  materi- 
ally aided  by  remembering  it. 

IRRITABILITY  OF  DIFFERENT  POINTS  OF  THE  SAME  NERVE. — The 
farther  from  the  muscle  the  nerve  is  stimulated,  the  lower  will  be  the 
original  irritability.  It  was  upon  this  fact  that  PfLiiger  predicated  his 
erroneous  avalanche  hypothesis :  that  a  nerve-wave  gathers  force  as  it 
passes  along  the  nerve-fiber.  The  true  theory  about  the  fact  is  that  the 
irritability  of  the  nerve  is  elevated  in  the  neighborhood  of  the  cross- 
section  by  the  passage  of  the  demarcation  current  through  that  por- 
tion. It  has  been  shown  by  mechanical  stimuli  that  the  uninjured 
nerve  has  an  equal  irritability  throughout  its  whole  length. 

Effect  of  Heat  on  Nerves. — Any  sudden  change  of  temperature 
acts  as  an  excitant  of  a  nerve.  A  temperature  below  24.8°  F.  or 
above  95°  F.  applied  to  a  motor  nerve  of  a  frog  calls  out  a  contrac- 
tion of  the  muscle. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  445 

If,  however,  a  nerve  be  gradually  frozen  it  will  regain  its  excita- 
bility upon  thawing.  When  a  nerve  is  cooled  in  the  case  of  the  frog 
the  irritability  persists  for  a  long  time.  If  a  nerve  of  a  frog  is 
heated  to  113°  F.  its  excitability  is  increased  and  then  diminished. 
In  the  case  of  a  man  who  plunged  his  elbow  into  a  freezing  mixture, 
so  as  to  greatly  cool  the  ulnar  nerve,  there  was  no  contraction,  but 
pain  in  the  parts  innervated  by  the  nerve. 

The  Transmission  of  the  Nerve-wave. — This  demands  that  the 
nerve-fiber  stimulated  be  entirely  sound.  It  has  the  following  phe- 
nomena: The  nerve-wave  passes  in  both  directions  in  both  sensory 
and  motor  nerves.  When  a  nerve  is  irritated  by  an  electrical  current 
the  electromotive  phenomenon  of  negative  variation  is  seen  in  both 
ends  of  the  nerve.  In  Bert's  experiment  of  fixing  the  end  of  a  rat's 
tail  in  a  wound  in  the  back  and  dividing  the  tail  at  its  root  after 
union  had  ensued  shows  that  the  stimulus  is  transmitted  both  ways 
in  the  case  of  sensory  nerves.  When  the  root  of  the  divided  tail  was 
irritated  there  followed  symptoms  of  pain,  showing  that  the  nerve 
impulse  of  sensation  was  transmitted  in  a  direction  opposite  to  the 
normal  one. 

This  fact  is  somewhat  difficult  of  explanation,  but  in  support  of 
it  comes  Kiihne's  classical  experiment.  This  investigator  takes  the 
sartorius  muscle  of  a  frog  and  separates  it  lengthwise,  beginning  at 
its  extremity,  so  that  two  small  tongues  are  formed.  Each  tongue 
receives  nervous  filaments  from  the  same  peripheral  branch.  If  one 
of  these  small  tongues  be  mechanically  stimulated  the  exciting  state 
of  the  motor  nervous  fiber  is  found  to  be  communicated  to  the  other 
small  tongue.  Since  the  second  small  tongue  was  excited  by  a  motor 
stimulus  to  the  first  one,  it  follows  that  the  conduction  occurred  in  a 
centripetal  direction  along  the  course  of  a  motor  nerve.  This  direc- 
tion is  different  from  that  of  normal  conduction,  for  the  nerve  which 
has  been  thus  excited  is  a  centrifugal  motor  nerve.  Therefore,  since 
the  motor  nerve  has  played  the  role  of  a  centripetal  conductor  in  this 
experiment,  it  follows  that  a  motor  nerve  can  conduct  an  excitation 
in  both  directions. 

Swiftness  of  the  Nerve-wave. — Compared  with  the  rapidity  of 
an  electrical  current,  the  nerve-current  is  immeasurably  slower.  In 
the  motor  nerves  of  a  frog  Helmholtz  made  it  about  88  feet  per  second. 
In  the  horse  Chauveau  found  it  to  be  about  227  feet  per  second  in  the 
motor  nerves  of  the  larynx  and  only  24  feet  in  the  motor  nerves  of  the 
oesophagus.  In  sensory  nerves  the  velocity  of  the  nerve-wave  is 
variable,  but  may  be  put  down  as  150  feet  per  second.  Cold  dimin- 


446  PHYSIOLOGY. 

ishes  the  swiftness  of  the  nerve-wave.  If  the  intensity  of  the  elec- 
trical stimulus  is  increased  the  swiftness  is  increased.  The  part  of 
a  nerve  in  a  state  of  an  electrotonus  slows  the  rapidity  of  the  nerve- 
current,  and  this  is  more  perceptible  as  the  duration  and  intensity 
of  the  polarizing  current  increases.  Catelectrotonus  favors  the 
rapidity  of  the  nerve-wave,  except  for  very  strong  currents,  where 
the  rapidity  of  the  nerve-current  is  arrested.  .  I  have  found  that 
stretching  a  nerve  lowers  the  rate  of  transmission  of  nerve-force. 
The  method  of  Helmholtz  to  measure  the  velocity  of  the  nerve-wave 
is  as  follows :  He  stimulated  a  motor  nerve  of  a  muscle  and  registered 


Fig.  107. — Curves  Illustrating  the  Measurement  of  the  Velocity  of  a  Nervous 
Impulse  (Diagrammatic).     (FOSTER.) 

To  be  read  from  left  to  right. 

The  same  muscle-nerve  preparation  is  stimulated  (1)  as  far  as  possible 
from  the  muscle  and  (2)  as  near  as  possible  to  the  muscle;  both  contractions 
are  registered  by  the  pendulum  myograph  exactly  in  the  same  way. 

In  1  the  stimulus  enters  the  nerve  at  the  time  indicated  by  the  line  a, 
the  contraction,  shown  by  the  dotted  line,  begins  at  b' ',  the  whole  latent 
period  therefore  is  indicated  by  the  distance  from  a  to  &'. 

In  2  the  stimulus  enters  the  nerve  at  exactly  the  same  time  (a) ;  the  con- 
traction, shown  by  the  unbroken  line,  begins  at  &;  the  latent  period  there- 
fore is  indicated  by  the  distance  between  a  and  b. 

.  The  time  taken  up  by  the  nervous  impulse  in  passing  along  the  length 
of  nerve  between  1  and  2  is  therefore  indicated  by  the  distance  between  6  and 
&',  which  may  be  measured  by  the  tuning-fork  curve  below. 

N.  B.— No  value  is  given  in  the  figure  for  the  vibrations  of  the  tuning- 
fork,  since  the  figure  is  diagrammatic,  the  distance  between  the  two  curves, 
as  compared  with  the  length  of  either,  having  been  purposely  exaggerated  for 
the  sake  of  simplicity. 

the  time  of  its  contraction  after  excitation.  After  a  while  the  same 
nerve  was  stimulated  at  a  point  nearer  its  distribution  with  the 
muscle.  Its  time  was  also  registered.  The  second  time  was  found 
to  be  shorter  than  the  first,  so  that  the  difference  between  it  and  the 
preceding  must  represent  the  time  required  between  the  two  excita- 
tion points  for  the  transmission  of  the  nerve-wave.  The  distance 
between  the  two  stimulated  areas  being  known,  one  can  very  readily 
calculate  the  swiftness  of  the  nervous  action. 

Excitability  and  Conductivity. — Excitability  of  a  nerve  is  its 
ability  to  react  to  the  irritations  received  by  it,  not  only  at  one  spot, 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


447 


but  through  its  whole  length.  Conductivity  is  the  property  of  trans- 
mitting its  whole  length,  up  to  terminal  extremity,  a  nerve-wave 
which  has  been  called  out  by  an  irritant.  If  a  part  of  a  trunk  of  a 
sciatic  nerve  of  a  frog  is  submitted  to  the  action  of  carbon  dioxide 
and  you  stimulate  that  part,  no  contraction  ensues.  But  if  you 
stimulate  the  nerve  above  this  point  a  tetanus  ensues.  Here  the 
nerve-wave  must  travel  through  the  part  affected  by  the  carbon 
dioxide.  Hence  it  is  inferred  that  conductivity  and  irritability  are 
separate  properties  in  a  nerve. 

Excitants  of  the  Nerve. — Nerve-excitants  are  all  those  forces 
which  modify  its  state.  There  are  electrical,  thermal,  mechanical, 
and  chemical  excitants.  From  the  fact  that  they  may  act  upon  a 


A 


a         d         ff 


N     f 


Fig.   108.— Scheme   of  Electrotonic   Excitability. 

The  nerve  (A~-«)  is  traversed  by  a  constant  current  in  the  direction  of  the 
arrow.  The  curve  shows  the  degree  of  increased  excitability  in  the  neighbor- 
hood of  the  cathode  (B)  as  an  elevation  above  the  nerve;  diminution  at  the 
anode  (A)  as  a  depression.  The  curve  i-h-g  shows  the  degree  of  excitability 
with  a  strong  current;  the  curve  f-e-d  with  a  medium  current,  and  the  curve 
c-l)-a  with  a  weak  current.  A,  is  anode.  B,  is  cathode. 

nerve  in  any  part  of  its  course,  they  are  frequently  designated  as 
general  stimuli. 

The  above  are  the  excitants  of  the  sensory  and  motor  nerve. 
However,  it  must  not  be  forgotten  that  in  the  normal  being  it  is  not 
these  forces  which  come  into  play  to  stimulate  to  activity  the  motor 
nerve.  The  normal  excitant  is  the  physiological  stimulus;  it  is  the 
will.  It  originates  within  the  nerve-centers,  from  where  it  is  trans- 
mitted to  the  motor  nerve.  Any  stimulus  when  applied  to  a  nerve 
causes  the  molecules  in  that  localized  area  to  vibrate  and  so  produce 
certain  electromotive  changes.  By  the  changes  set  up  in  this  par- 
ticular area  of  nerve,  the  contiguous  parts  are  necessarily  also 
brought  into  activity  by  reason  of  nerve-conduction.  By  many 
authors  this  transmission  of  changes  along  the  course  of  the  nerve  so 
as  to  act  as  excitants  is  known  as  the  true. physiological  stimulus. 


448  PHYSIOLOGY. 

Thus,   the   vibrations   in   each   segment   perform   the   function   of 
excitant  for  each  succeeding  segment. 

ELECTRICAL  EXCITANTS. — This  form  of  stimulus  is  surely  the 
most  important  to  study  and  is,  perhaps,  the  one  that  is  most  com- 
plex. The  electrical  stimulus  may  consist  of  either  the  constant  or 
interrupted  current.  The  stimulation  of  the  nerve  may  be  direct, 
as  when  the  electrodes  are  applied  to  the  nerve.  There  are  two 
kinds  of  currents  used:  the  induction  current  and  the  galvanic  cur- 
rent. I  shall  take  up  the  constant  current.  The  passage  of  a  con- 
stant current  through  a  nerve  changes  its  irritability  and  conduc- 
tivity and  the  nerve  is  said  to  be  in  a  state  of  electrotonus ;  the 
positive  pole  is  the  anode  and  the  negative  pole  is  the  cathode.  The 
nerve  about  the  positive  pole  is  said  to  be  in  a  state  of  anelectrotonus, 
the  parts  about  the  cathode  are  said  to  be  in  a  state  of  cate'lectro- 
tonus.  When  the  current  runs  up  the  nerve,  the  anode  nearest  the 
muscle,  then  the  current  is  said  to  be  ascending.  In  the  descending 
current  the  anode  is  farthest  away  from  the  muscle.  The  parts  at 
the  anode  are  decreased  and  at  the  cathode  increased  in  excitability. 
When  a  constant  current  passes  through  the  motor  nerve  a  contraction 
takes  place  only  at  the  closing  and  at  the  opening  of  the  current. 
These  opening  and  closing  contractions  occur,  according  to  Pniiger, 
as  follows  ("No"  means  rest  for  muscle;  "Yes"  means  contraction 
of  muscle) : — 


CURRENT. 

DESCENDING. 

ASCENDING. 

Weak  
Medium                

MAKE. 

Yes. 
Yes. 
Yes. 

BREAK. 

No. 
Yes. 
No. 

MAKE. 

Yes. 
Yes. 
NO.           | 

BREAK. 

No. 
Yes. 
Yes. 

Strong    .    . 

These  laws  are  explained  as  follows : — 

With  Ascending  Current. — 1.  If  the  current  is  strong  the  anelec- 
trotonic  part  of  the  nerve  loses  its  conductivity,  the  stimulus  of  the 
closing  is  not  transmitted  to  the  nerve  and  no  contraction  follows. 
At  the  opening  of  the  current  the  anelectrotonus  disappears,  stimu- 
lation is  produced  at  the  anode,  and  the  muscle  contracts. 

2.  If  the  current  is  moderate  the  conductivity  of  the  anelectro- 
tonic  part  is  not  affected  and  the  stimulation  produced  at  the  open- 
ing and  closing  of  the  current  is  transmitted  to  the  muscle,  which 
contracts. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  449 

3.  With  weak  currents  the  stimulation  is  only  active  at  the 
point  farthest  from  the  muscle,  and  the  closing  produces  contraction. 

With  Descending  Current. — 1.  With  strong  currents  the  stimulus 
of  closing  produces  a  contraction,  but  the  stimulation  of  opening 
acting  on  the  anelectrotonic  part  has  no  effect. 

2.  With  moderate  current  contraction  ensues  on  the  opening 
and  closing  of  the  current  for  the  same  reasons  as  in  the  case  of  the 
ascending  current. 

3.  With  weak  current  the  onset  of  catelectrotonus  is  a  more 
powerful  stimulant  than  the  disappearance  of  the  anelectrotonus ; 
the  effect  of  the  latter  is  too  slight  to  manifest  any  action. 

MECHANICAL  IRRITANTS. — Nerves  respond  to  mechanical  stimu- 
lants only  when  the  disturbance  which  reaches  them  possesses  a 
certain  suddenness.  By  this  suddenness  there  is  produced  a  change 
in  the  form  of  the  nerve-particles.  Thus,  the  blow,  pressure,  pinch- 
ing, or  section  must  be  accomplished  quickly;  if  a  nerve  be  squeezed 
slowly  it  may  be  completely  destroyed  without  having  provoked  move- 
ment in  the  muscle  innervated  by  the  same. 

CHEMICAL  EXCITANTS  OF  THE  NERVE. — Certain  substances  which 
act  with  a  certain  degree  of  rapidity  upon  a  nerve-fiber  are  capable  of 
acting  as  nerve-stimuli.  Nearly  all  chemical  substances,  other  than 
very  dilute  salts  and  very  weak  acid  solution,  excite  the  nerves. 
Glycerin  is  a  very  energetic  nervous  stimulant.  This  fact  is  interest- 
ing, since  glycerin  is  not  a  chemical  excitant  of  muscular  tissues.  It 
owes  its  function  to  its  dehydrating  properties. 

Seat  of  Reflex  Action. — Experiments  prove  that  the  transforma- 
tion of  feeling  into  movement  takes  place  in  the  spinal  cord.  This 
doctrine  is  universally  accepted  to-day. 

The  fundamental  experiment  is  as  follows:  A  frog  is  decapi- 
tated. WThen  one  of  its  feet  is  touched  the  same  is  at  once  with- 
drawn and  movements  of  escape  are  made.  As  a  probe  is  passed  into 
the  spinal  cord  to  destroy  the  same,  convulsive  movements  of  all  the 
muscles  are  immediately  provoked.  The  aspect  of  the  frog  is  now 
altogether  different.  It  has  become  flabby,  inert,  and  it  no  longer 
reacts  to  the  different  excitants.  Nevertheless,  its  muscles  and 
nerves  in  themselves  are  irritable.  Muscles  contract  when  an  elec- 
trical irritant  is  applied  either  to  the  muscle  (direct  excitation)  or  to 
the  nerve  (indirect  excitation). 

What  was  destroyed  in  the  frog  and  prevented  the  transforma- 
tion of  feeling  into  movement  was  the  nerve-cell:  an  anatomical  ele- 
ment which  becomes  absolutely  necessary  for  such  transformation. 

29 


450  PHYSIOLOGY. 

Reflex  Action. — A  motor  reflex  act  is  the  transmission  of  an 
irritation  by  the  neuraxon  of  a  sensory  neuron  to  the  dendrons  of  a 
motor  neuron  and  by  its  neuraxon  in  turn  to  the  muscle. 

The  functions  of  the  gray  substance  of  the  nervous  centers  can 
be  known  only  through  reflex  movements;  so  that,  to  study  reflex 
action  is  to  study  the  nervous  centers. 

From  a  knowledge  of  the  principles  of  a  reflex  action  it  will  be 
seen  that  three  stages  must  be  considered:  1.  The  external  excitation 
which  goes  to  excite  the  nervous  centers  through  the  sensitive  nerves 
as  a  medium.  2.  The  excitation  of  the  nervous  centers  which  re- 
ceive the  irritation  and  then  transform  and  modify  it;  through  the 
medium  of  the  motor  nerves  it  is  communicated  to  the  muscles. 
3.  The  contraction  of  the  muscle  thus  innervated. 

OTHER,  SEATS. — It  is  not  only  in  the  spinal  cord  properly  so 
called  that  there  are  reflex  acts.  There  are  some  in  the  medulla 
dblongata,  in  the  pons,  and  in  the  gray  parts  of  the  brain. 

The  physiological  study  of  strychnine  shows  what  intimate  con- 
nections exist  between  the  different  parts  of  the  spinal  cord.  The 
irritation  of  any  point  whatever  of  the  periphery,  being  transmitted 
to  the  spinal  cord  by  a  sensitive  nerve,  goes  to  provoke  at  once  the 
activity  of  the  whole  organ. 

The  initial  stimulation  for  a  reflex  action  may  arise  from  any 
sensory  nerve,  whether  of  special  sense,  touch,  or  visceral  supply.  But 
there  are  some  which  generate  a  more  active  reflex  movement,  among 
which  may  be  mentioned  those  of  the  palm  of  the  hand  and  the  sole 
of  the  foot.  The  quality  and  nature  of  the  stimulus  used  has  an 
influence  on  the  reflex.  Thus,  tickling  the  auditory  meatus  produces 
cough;  excessive  sunlight  acting  on  the  retina  causes  sneezing. 
Stimulation  of  a  sensory  nerve-trunk  in  any  part  of  its  course  calls 
out  a  reflex  action,  but  the  movement  in  this  case  is  much  less 
energetic  and  its  character  altered.  In  such  a  case  the  stimulation 
causes  movement  in  one  or  more  muscles,  while  stimulation  of  the 
skin  surface  innervated  by  the  same  nerve  produces  movements 
which  have  a  peculiar  character  of  co-ordination.  To  produce  a 
reflex  action  the  application  of  the  stimulus  must  be  sufficiently 
rapid. 

Any  agent  which  produces  a  slow  and  gradual  change  in  the 
nerve  is  without  effect.  Some  experimentalists  have  found  a  differ- 
ence between  the  reflex  of  chemical  and  mechanical  stimulation. 
When  the  reflex  center  has  a  greater  or  less  excitability,  then  the 
stimulation  produces  greater  or  less  results.  Every  center  which 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          451 

gives  origin  to  a  motor  nerve  may  be  looked  upon  as  a  reflex  center. 
The  excitability  of  the  reflex  centers  is  increased  when  their  connec- 
tion with  the  cerebrum  is  cut  off  or  when  the  latter  centers  are 
inactive.  Hence  after  decapitation,  removal  of  the  brain,  section  of 
the  oblong  medulla,  or  section  of  the  spinal  cord,  the  centers  below 
the  section  have  greatly  increased  activity  in  their  reflexes.  Set- 
schenow  has  shown  that  mainly  in  the  optic  thalami  and  corpora 
striata  are  seated  centers  inhibiting  the  activity  of  the  spinal  reflex 
centers. 

Eeflex  excitability  is  much  greater  in  young  animals  than  in 
adults.  This  explains  the  quickness  with  which  slight  causes  pro- 
duce convulsions  in  the  infant.  Eeflex  activity  is  greater  in  the 
summer  than  in  the  winter.  Certain  toxic  agents  have  an  effect  on 
the  reflexes.  Thus,  atropine,  bromides,  chloral,  chloroform,  and  ether 
reduce  reflex  activity,  while  strychnine  greatly  excites  it.  Chloro- 
form is  poisonous  to  every  living  cell,  whether  of  plant  or  animal 
life.  Strychnine  is  only  poisonous  to  the  nerve-cell,  not  to  the 
plant-cell. 

Every  time  that  intellectual  action  is  suppressed  then  are  the 
reflexes  more  manifest.  A  person  asleep  has  more  energetic  reflex 
actions  than  a  person  who  is  awake.  In  somnambulism  the  action  of 
the  will  is  nearly  suppressed,  while  the  reflex  excitability  of  the  cord 
is  enormously  increased. 

On  the  other  hand,  a  person  by  exercising  a  strong  will  can 
arrest  certain  reflexes.  Thus,  the  conjunctival  reflex  can  be  pre- 
vented by  the  will  of  a  courageous  person.  Up  to  a  certain  point  a 
person  is  able  to  resist  sneezing  or  coughing,  which  are  certainly 
typical  reflex  movements. 

SWIFTNESS  OF  EEFLEX  ACTIONS. — Helmholtz  succeeded  in  meas- 
uring by  the  graphic  method  the  swiftness  of  the  spinal  actions.  By 
him  it  was  ascertained  that  the  excitation  travels  in  the  spinal  cord 
at  the  rate  of  about  twenty-four  feet  per  second. 

LAWS  OF  EEFLEX  ACTIONS. — They  are  the  law  of  localization 
and  that  of  irradiation.  One  other  accessory  law  will  be  added :  the 
law  of  co-ordination. 

Law  of  Localization. — If  any  sensitive  region  be  excited,  the  first 
reflex  movement  which  will  be  produced  will  bear  upon  the  muscles 
near  the  sensitive  region  excited. 

Thus,  if  the  foot  of  a  frog  be  very  lightly  touched,  the  muscles 
of  that  foot  will  respond  reflexly.  If  the  conjunctiva  be  touched, 
the  reflex  movement  will  be  in  the  orbicular  muscles. 


452  PHYSIOLOGY. 

Law  of  Irradiation. — When  an  excitation  has  produced  a  reflex 
movement  in  the  muscles  of  one  side  by  a  first  degree  of  irradiation, 
there  will  be  reflex  movements  in  the  corresponding  muscles  of  the 
opposite  side.  Cutaneous  constriction  by  cold  applied  to  the  right 
hand  determines  constriction  of  the  vasomotors  of  the  left  hand  as 
well.  These  are  examples  of  the  type  known  as  transverse  irradiation. 

If  the  excitation  be  more  intense,  the  movement  is  spread  into 
the  muscles  situated  above  and  below  the  point  of  excitation.  This 
represents  the  longitudinal  irradiation. 

Law  of  Co-ordination. — The  law  of  co-ordination  or  adaptation 
of  the  reflex  actions  in  decapitated  animals  is  very  striking.  If  a 
drop  of  acetic  acid  be  placed  upon  the  back  of  a  decapitated  frog  the 
animal  will  make  such  movements  with  the  feet  as  will  show  that 
it  seems  to  want  to  free  itself  from  the  substance  which  irritates  it. 
They  are  not  blind  movements,  but  such  as  seem  to  be  adapted  to  an 
end  and  are  co-ordinated. 

Tonus  of  Spinal  Cord. — It  cannot  be  denied  that,  in  the  normal 
state,  there  is  always  a  certain  spinal  tonus.  That  is  to  say,  an 
active  state  of  the  cord  which  is  not  provoked  by  any  immediate 
excitation.  All  of  the  muscles  of  the  organism,  striated  as  well  as 
smooth,  are  always  in  a  state  intermediate  between  relaxation  and  con- 
traction. This  state  of  semiconstriction,  of  semi-activity,  is  governed 
by  the  spinal  cord.  When  the  spinal  cord  is  destroyed,  immediately 
all  of  the  muscles  of  the  body  relax  and  their  tonus  ceases. 

Influence  of  the  Blood. — If  a  limb  be  separated  from  the  rest  of 
the  organism,  and,  consequently,  receives  no  nutritive  blood-current, 
nevertheless  the  function  of  the  nerve  persists. 

By  making  Stenon's  experiment  (tying  the  abdominal  aorta),  at 
the  end  of  twenty  minutes,  or  an  hour  at  the  most,  it  will  be  found 
that  sensibility  and  motility  disappear  in  the  abdominal  members. 
Yet,  though  the  deprivation  of  blood  be  complete,  still  there  is 
preservation  of  the  nervous  activity  for  some  time. 

.  By  using  on  man  the  ligature  and  then  compressing  the  limb  by 
an  Esmarch  bandage  interesting  observations  upon  the  influence  of 
anaemia  are  made.  During  the  first  twenty  minutes  the  arm  is  sensi- 
tive and  the  cutaneous  excitations  are  plainly  perceived.  Likewise 
the  motor  nerves  can  still  command  the  movements  of  the  muscles. 

Soon,  however,  the  sensibility  becomes  obtuse;  the  voluntary 
movements  take  place  only  incompletely,  without  force,  and  slowly. 
Next  the  sensibility  disappears  so  completely  that  the  strongest  elec- 
trical excitations  are  not  felt.  Because  of  the  powerlessness  of  the 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          453 
/ 

motor  nerves,  the  limb  feels  limp  and  inert  as  if  it  were  completely 
paralyzed. 

This  state  of  death  of  the  nerves,  from  anaemia,  contrasts  with 
the  survival  of  the  muscles.  The  nerve  dies  before  the  muscle,  but 
much  later  than  the  nervous  centers. 

EXCITING  EFFECTS  OF  ANEMIA. — However  it  may  be,  anaemia, 
which  makes  the  functions  of  the  nerve  finally  disappear,  begins  at 
first  by  overexciting  it.  Thus,  the  first  effects  of  anaemia  are  marked 
by  an  increase  of  excitability.  If  it  be  a  sensory  member,  anaemia  of 
it  provokes  extremely  lively  pains.  Physicians  have  long  been  ac- 
quainted with  painful  anaemiae.  It  is  anaemia,  not  absolute,  but  rela- 
tive, which  is  often  the  cause  of  intense  peripheral  pains.  Thus,  in 
symmetrical  gangrene  of  the  extremities  (Baynaud's  disease),  which 
is  characterized  by  complete  cessation  of  the  circulation  in  the  affected 
areas,  the  pain  is  very  acute.  There  is  extreme  hyperaesthesia,  prob- 
ably due  to  nervous  anaemia. 

Physiology  of  the  Spinal  Cord  and  its  Nerves. 

The  spinal  cord  represents:  1.  A  great  conductor  whose  extent 
lies  between  the  brain  and  periphery  of  the  body.  Along  it  are 
transmitted  centrifugal  as  well  as  centripetal  actions;  the  former 
carry  volitional  impulses  to  the  muscles,  the  latter  impressions  from 
the  sensitive  surfaces  to  the  brain.  By  reason  of  the  spinal  cord  having 
in  its  composition  innumerable  nervous  cells,  it  becomes  a  co-ordinator 
of  the  actions  which  pass  over  it. 

2.  The  spinal  cord  represents  a  true  nervous  center.  It  may  be 
either  an  important  center  of  reflex  phenomena  in  that  its  cells  unite 
centripetal  fibers  with  centrifugal  ones,  or  it  may  possess  the  role 
of  acting  as  a  special  center  of  the  special  functions. 

Cord  as  a  Conductor. — The  law  of  Bell  is  enunciated  as  follows : 
"Of  the  roots  which  issue  from  the  spinal  cord,  the  anterior  are  those 
of  motion  and  the  posterior  those  of  sensation." 

This  law  is  very  clearly  demonstrated  by  the  so-called  Miiller 
frog.  If  the  last  four  anterior  spinal  roots  in  the  cauda  equina  of  a 
frog  are  cut  off  at  the  right,  and  the  four  last  posterior  roots  are  cut 
off  at  the  lefty  the  animal  after  recovering  from  the  operation  will 
present  interesting  conditions.  The  right  lower  leg  will  be  para- 
lyzed; that  is,  deprived  of  voluntary  motion.  The  left  lower  leg  will 
be  anaesthetic  instead.  It,  will  be  deprived  of  sensation,  but  still 
possess  motion.  Therefore,  the  anterior  spinal  roots  are  motor  and 
the  posterior  ones  sensory. 


454 


PHYSIOLOGY. 


Irritation  of  the  posterior  roots,  or  of  their  central  stumps, 
determines  sensations.  These  sensations  are  sharp  pains  in  the 
regions  innervated  by  the  particular  nerve.  Excitation  of  the 
peripheral  stump  is  without  any  effect. 

Irritation  of  the  anterior  roots,  or  of  their  peripheral  stumps, 
determines  movements.  These  movements  are  of  the  nature  of  con- 
vulsive cramps  in  the  particular  muscles  innervated.  Excitation  of 
the  central  stumps  is  not  followed  by  any  effect. 

Cutting  off,  or  the  complete  destruction,  of  the  posterior  roots 
causes  the  loss  of  tactile,  thermal,  and  painful  sensibilities;  also  of 
muscular  sensation  in  the  parts  where  they  are  distributed.  Sec- 
tion of  the  anterior  roots  wholly  paralyzes  the  muscles  innervated  by 
them. 


Fig.  109. — Diagram  of  the  Roots  of  a  Spinal  Nerve  Showing  Effect 
of  Section.     (LANDOIS.) 

The  black  represents  the  degenerated  parts.  A,  Section  of  the  nerve- 
trunk  beyond  the  ganglion.  B,  Section  of  the  anterior  root.  C,  Section  of 
the  posterior  root.  D,  Excision  of  the  ganglion,  a,  Anterior  root,  p,  Pos- 
terior root,  g,  Ganglion. 

APPAKENT  CONTKADICTIO^. — In  demonstrating  Bell's  law  there 
occasionally  are  seen  results  which  seem  to  contradict  that  law,  but 
instead  they  really  confirm  it.  It  is  found  that  in  stimulating  the 
anterior  (motor)  root  with  electricity  the  animal  sometimes  gives 
evidences  of  pain.  This  same  thing  may  occur  also  after  cutting  it 
in  the  middle  and  then  stimulating,  not  the  central,  but  the 
peripheral  stump.  Bernard  has  explained  the  sensibility  of  the 
anterior  root  by  admitting  that  the  recurrent  sensitive  fibers.,  which, 
taking  their  departure  from  the  posterior  roots,  run  back  from  the 
periphery  to  the  center  on  the  anterior  root.  If  the  posterior  root 
be  cut  near  to  the  spinal  cord,  sensibility  in  the  corresponding 
anterior  root  wholly  disappears. 

The  spinal  roots  united,  those  of  sensation  with  those  of  motion, 
constitute  the  mixed  spinal  nerves.  They  furnish  the  different  parts 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  455 

of  the  body  in  which  they  are  distributed  with  both  sensibility  and 
motion.  Consequently  the  section  of  many  spinal  nerves  leads  to 
anaesthesia  and  paralysis  of  the  parts  innervated.  In  the  recently 
cut  nerves,  the  central  as  well  as  peripheral  stumps  are  excitable  by 
stimulants,  the  former  causing  pain,  the  latter  contractions. 

Ganglion. — The  posterior  root,  before  joining  the  anterior, 
forms  the  ganglion.  The  function  of  this  ganglion  is  its  trophic  influ- 
ence, discovered  by  Waller  and  afterward  proved  by  Bernard  and 
others.  When  an  anterior  root  is  cut  the  peripheral  stump  becomes 
atrophied,  whereas  the  central  stump  remains  entire.  The  latter 
retains  its  vitality,  since  it  is  still  in  connection  with  its  trophic 
center  in  the  cells  of  the  anterior  horn  of  the  gray  matter. 

On  the  contrary,  when  a  posterior  root  is  cut  between  the  spinal 
cord  and  the  ganglion  the  peripheral  stump  remains  entire,  while  the 
central  stump  becomes  atrophied.  The  ganglia  of  the  posterior 
spinal  roots  have,  therefore,  the  office  of  trophic  centers  over  the 
sensory  nerves;  the  trophic  centers  for  the  motor  nerves  lie  within 
the  cord  itself  and  are  none  other  than  the  large,  multipolar  cells  of 
the  anterior  horns. 

The  anterior  roots  contain  different  centrifugal  fibers — motor 
fibers,  vasomotor  fibers,  sweat,  and  inhibitory  fibers  of  the  splanch- 
nics.  The  motor  fibers  take  their  origin  in  the  cells  of  the  anterior 
horns,  while  other  centrifugal  fibers  are  united  to  the  cerebral  cortex. 
As  to  the  vasomotor  fibers,  they  have  their  centers  of  origin  in  the 
medulla  oblongata  and  cord  to  penetrate  the  anterior  roots.  They 
probably  do  this  without  entering  into  communication  with  the  cells 
of  the  anterior  horns. 

The  posterior  roots  have  centripetal  reflex  fibers.  These  leave 
the  skin,  muscles,  and  other  organs;  penetrate  the  spinal  cord;  and 
are  in  direct  connection  with  the  reflex  centers  located  partly  in  the 
cord  itself  and  partly  in  the  medulla  oblongata,  pons,  corpora  quadri- 
gemina,  cerebellum,  and  optic  thalami.  The  other  sensory  and 
sense-  fibers  enter  the  cord  by  way  of  the  posterior  roots  to  ascend 
toward  the  cerebral  cortex.  Here  are  received  the  several  conscious 
sensations :  touch,  pressure,  temperature,  pain,  and  muscular  sense. 

Path  of  Transmission  of  Voluntary  Motion. — Voluntary  motor 
excitation  is  transmitted  from  the  cerebral  cortex  to  the  nerve-cells 
of  the  anterior  horns  by  way  of  the  anterior  and  lateral  columns. 
These  columns,  as  a  whole,  do  not  participate  in  conduction,  but  only 
the  anterior  pyramidal  tracts  of  the  anterior  columns  and  the  crossed 
pyramidal  tracts  of  the  lateral  columns. 


456  PHYSIOLOGY. 

As  the  student  knows,  the  crossed  pyramidal  tracts  do  not  decus- 
sate in  the  cord,  but  in  the  medulla  oblongata.  The  direct  pyramidal 
tract  does  not  decussate  in  the  medulla.,  but  in  the  spinal  cord  by  the 
anterior  commissure. 

When  the  spinal  cord  is  completely  severed  the  voluntary  move- 
ments for  all  of  the  muscles  below  the  point  of  section  are  absolutely 
abolished. 

Path  of  Conscious  Sensations. — The  sensations  of  touch  and 
muscular  sense  are  transmitted  by  the  posterior  roots  and  traverse 
the  posterior  columns  to  the  brain. 

Muscular  sense  is  transmitted  mainly  by  the  posterior  columns. 
The  cerebellar  tract  also  contains  fibers  which  conduct  muscle-sense. 
Tactile  and  muscular  sensations  are  abolished  by  locomotor  ataxia. 

One-sided  section  of  the  posterior  and  lateral  columns  causes : 
(a)  suppression  of  skin  sensations,  or  anesthesia,  in  the  whole  half 
of  the  body  innervated  by  nerves  which  enter  the  cord  on  the  side  of 
section;  (b)  loss  of  motion  on  side  of  section.  There  is  very  fre- 
quently observed  on  the  side  of  hemisection  a  zone  of  hypersesthesia ; 
this  is  due  either  to  removal  of  inhibition  on  that  side  or  inflamma- 
tory irritation  of  the  central  extremity  of  the  cut  cord. 

It  has  been  shown  by  Woroschilof?  in  Ludwig's  laboratory  that 
the  lateral  columns  are  a  pathway  for  sensory  impulses.  I  have 
shown  with  Dr.  Eobert  M.  Smith  similar  results  in  a  series  of  sections 
of  the  lumbar  part  of  the  spinal  cord. 

Section  of  the  posterior  and  lateral  columns  does  not  exercise 
any  influence  upon  sensibility  to  pain  and  temperature.  But  this 
is  not  the  case  when  the  gray  matter  is  cut;  so  that  it  must  be 
inferred  that  these  impulses  ascend  through  the  gray  substance  to 
the  brain. 

Syringomyelia  is  the  term  applied  to  that  condition  when  there 
is  complete  abolition  of  the  conduction  of  pain  and  temperature.  It 
is  due  to  vacuolation  of  the  gray  matter  of  the  cord. 

FIBERS  FROM  THE  CENTERS  OF  THE  MEDULLA  OBLONGATA. — The 
vasomotor  nerves,  which  come  from  a  center  seated  in  the  medulla 
oblongata,  run  down  the  lateral  column  to  penetrate  into*  the  gray 
substance  and  anterior  roots.  Hence,  section  of  the  lateral  columns 
produces  a  dilatation  of  the  arterioles  innervated  by  vasoconstrictors, 
which  leave  the  cord  below  the  point  of  section. 

The  nerves  leaving  the  respiratory  center  also  run  through  the 
lateral  columns  and  enter  the  gray  substance,  to  communicate  with 
it  and  leave  by  the  anterior  roots. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          457 

In  the  middle  third  of  the  lateral  columns  I  have  found  running 
both  sweat  and  inhibitory  fibers.  Both  sets  of  fibers  I  have  discovered 
decussate :  the  former  in  the  spinal  cord,  the  latter  in  the  medulla. 

Skin  Reflexes. — The  most  important  skin  reflexes  in  man  are : — 

1.  THE  PLANTAR  REFLEX,  which  is  caused  by  tickling  the  sole 
of  the  foot.     The  involved  center  lies  in  the  lumbar  cord. 

2.  THE  CREMASTERIC  REFLEX. — If  the  skin  of  the  upper  and 
inner  surface  of  the  thigh  in  man  be   excited  the  corresponding 
testicle  will  be  seen  suddenly  to  rise  by  contraction  of  the  cremaster 
muscle.     Its  center  lies  between  the  first  and  second  lumbar  nerves. 

3.  THE  ABDOMINAL  REFLEX  is  a  contraction  of  the  abdominal 
muscles  caused  by  a  sharp  push  of  the  finger.    Its  center  lies  between 
the  eighth  and  twelfth  dorsal. 

4.  THE  EPIGASTRIC  REFLEX. — If  the  skin  between  the  fourth, 
fifth,  and  sixth  intercostal  spaces  be  irritated,  contractions  of  the 
rectus  abdominis  of  the  same  side  will  follow.     The  center  is  between 
the  fourth  and  eighth  dorsal. 

5.  SCAPULAR  REFLEX. — An  irritation  of  the  skin  covering  the 
scapulae  may  cause  contraction  of  the  shoulder-muscles.     Its  center 
is  between  the  seventh  cervical  and  second  dorsal  nerves. 

Tendon  Reflexes. — 1.  ANKLE-CLONUS. — When  the  sole  of  the 
foot  is  pressed  upon  by  the  hand,  then  the  gastrocnemius  contracts, 
and  if  the  pressure  is  continued  there  may  be  several  clonic  contrac- 
tions. Ankle-clonus  is  never  found  in  health. 

2.  PATELLAR  REFLEX. — When  a  tap  is  made  on  the  tendon  of 
the  quadriceps  just  below  the  patella,  the  foot  jumps  upward. 

The  tendon  reflexes  are  not  true  reflexes,  but  are  due  to  a  direct 
stimulant  action  on  the  muscle  itself.  But  a  reflex  arc  is  necessary 
to  keep  the  muscles  in  a  state  of  tonus  that  the  tendon  reflexes  may 
take  place. 

Centers  in  the  Spinal  Cord. — The  spinal  cord  presides  over  the 
movements  of  the  anus,  bladder,  and  genital  apparatus  by  .means  of 
three  centers  located  one  above  the  other. 

The  ano-spinal  center  is  found  in  the  dog  near  the  fifth  lumbar 
vertebra.  From  this  center  emanate  fibers  which,  with  the  sacral 
nerves,  go  to  animate  the  sphincter  of  the  anus.  Irritation  of  this 
center,  especially  by  disease,  brings  on  spasm  of  the  sphincter,  with 
difficulty  in  passing  the  faeces.  Destruction  of  the  center  causes 
paralysis  of  the  sphincter  and  incontinence  of  faeces. 

In  paraplegics  (those  affected  with  paralysis  of  the  lower  limbs 
from  cord  lesion),  spinal  incontinence  or  the  involuntary  passage  of 


458  PHYSIOLOGY. 

the  faeces  may  be  observed.  In  addition,  there  is  a  protracted  and 
invincible  constipation.  The  former  condition  depends  upon  the 
destruction  of  the  spinal  center,  while  the  latter  comes  from  paresis 
of  the  intestine  in  the  region  of  the  colon  and  rectum. 

The  vesico-spinal  center  in  dogs  is  found  between  the  third  and 
fifth  lumbar  vertebra?.  When  it  or  the  nerves  which  take  their  de- 
parture from  it  are  stimulated  there  are  energetic  and  painful  contrac- 
tions of  the  body  and  neck  of  the  bladder. 

In  apoplectics  there  is  often,  first,  ischuria  (retention  of  urine), 
which  seldom  comes  from  irritative  or  nervous  spasm  of  the 
sphincter,  but  more  frequently  from  paralysis  limited  to  the  detrusor 
nerves  only.  Afterward  there  is  enuresis  (incontinence  of  urine), 
from  paralysis  also  of  the  nerves  of  the  sphincter. 

The  genito-spinal  center  is  to  be  found  in  the  spinal  cord  at  the 
level  of  the  fourth  lumbar  vertebra.  If  excited  by  stimuli  it  pro- 
duces contractions  of  the  lower  part  of  the  rectum,  bladder,  and,  if 
the  animal  be  a  female,  the  uterus.  In  addition,  if  the  spinal  cord 
be  cut  between  the  dorsal  and  lumbar  parts,  tickling  of  the  mucous 
membrane  of  the  glans  penis  of  the  dog  determines  by  reflex  action 
an  erection.  Erection  is  no  longer  obtained  if  the  lumbar  cord  be 
destroyed.  Goltz  and  Freusberg  have  observed  in  a  bitch,  whose 
spinal  cord  was  cut  at  the  level  of  the  last  lumbar  vertebra,  the  mani- 
festations of  desire,  conception,  gestation,  delivery,  and  lactation  to 
take  place  just  as  in  a  sound  bitch. 

In  obstetrical  wards  women  are  delivered  while  in  the  anaes- 
thetic sleep  produced  by  ether,  chloroform,  or  other  anesthetics. 

These  various  facts  show  that  the  center  of  the  movements  of 
the  uterus  is  found  in  the  spinal  cord,  and  not  in  the  brain. 

The  sudorific  centers  are  seated  in  the  spinal  cord.  The  spinal 
cord  has  minor  vasomotor  centers  for  the  vessels  of  the  parts  it  inner- 
vates. In  fact,  cutting  of  the  cord  produces  hyperaBmia  and  eleva- 
tion of  temperature  in  the  paralyzed  parts.  This  is  due  to  the 
paralysis  of  the  vessels  there.  The  constrictors  are  paralyzed. 

Electrical  excitations  of  the  peripheral  stump  lowers  the  tem- 
perature in  the  parts  innervated  by  constricting  the  lumen  of  the 
corresponding  arterioles.  The  vasomotor  fibers,  emanating  from  the 
spinal  column,  rejoin  the  vessels  either  directly  or,  more  commonly, 
by  means  of  branches  of  the  sympathetic. 

The  cilio-spinal  center  is  seated  in  the  lower  cervical  cord  and 
down  the  dorsal  cord  to  the  third  dorsal  vertebra.  There  fibers 
emerge  by  the  anterior  root  of  the  two  lower  cervical  and  the  two 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  459 

upper  dorsal  nerves  and  go  into  the  cervical  sympathetic  to  the  dilat- 
ing fibers  of  the  iris.  Pinching  the  skin  of  the  neck  will  dilate  the 
pupils :  another  skin  reflex. 

Physiology  of  the  Medulla  and  its  Nerves. 

The  medulla  ollongata,  or  lull),  like  the  spinal  cord,  is  an  organ 
of  transmission,  or  conduction,  but  at  the  same  time  it  is  a  center  of 
particular  and  very  important  functions. 

Double  Conduction. — Like  the  spinal  cord,  the  medulla  carries 
centripetal,  or  sensory  actions,  and  centrifugal,  or  motor  actions. 
The  former  are  conveyed  by  means  of  its  posterior  part;  the  latter 
by  the  anterior  part. 

The  centripetal,  sensory  conduction  is  crossed  or  decussated 
along  the  floor  of  the  fourth  ventricle.  The  centrifugal,  motor 
conduction  accomplishes,  instead,  its  decussation  in  the  pyramids 
of  the  medulla,  where  the  right,  lateral  fibers  pass  to  the  left,  and 
vice  versa.  This  decussation  of  the  fibers  is  much  more  complete 
in  man  than  in  animals.  So  much  is  this  so  that  in  man  a  lesion 
which'  destroys  one-half  of  the  medulla  brings  on  complete  hemi- 
plegia  of  the  opposite  side;  in  animals  a  similar  lesion  never  pro- 
duces hemiplegia,  but  only  paresis.  Equally,  in  animals  this  same 
lesion  does  not  entirely  abolish  sensibility  in  the  opposite  side  of  the 
body.  The  gray  substance  of  the  opposite  side  connects  the  parts 
lying  over  and  under  the  lesion,  and  so  conducts  the  sensory  im- 
pressions. 

Bulbar  Nerves. — From  the  medulla  oblongata  take  their  origin 
and  departure  ten  pairs  of  nerves:  the  lulbar  nerves.  Each  nerve 
has  a  gray  nucleus.  The  nuclei  on  the  right  side  are  connected  with 
those  on  the  left  and  all  have  their  location  along  the  gray  substance 
of  the  floor  of  the  fourth  ventricle.  The  fibers  which  connect  these 
nuclei  of  origin  with  the  superior  cranial  centers  are  also  crossed  on 
the  way. 

Centers. — The  medulla,  with  its  gray  substance  and  especially 
with  the  gray  nuclei  of  the  nerves  which  issue  from  it,  becomes  a 
center  of  very  important  functions. 

First,  it  is  a  respiratory  center.  This  center  is  found  toward  the 
inferior  angle  of  the  fourth  ventricle,  a  little  back  of  and  lateral  to 
the  source  of  the  vagi  nerves.  It  is  composed  of  two  lateral  halves, 
each  of  which  can  take  the  place  of  the  other  in  function.  This 
center  is  about  two  and  one-half  millimeters  in  size. 


460  PHYSIOLOGY. 

A  lesion  affecting  both  respiratory  centers  causes  the  sudden 
death  of  a  warm-blooded  animal.  Therefore  this  region  of  the 
fourth  ventricle  has  been  called  the  vital  knot.  In  fact,  a  blow  from 
a  stick  upon  the  back  part  of  the  head  or  upon  the  nape  of  the  neck, 
also  a  thrust  from  a  sharp  stiletto  between  the  back  of  the  head  and 
the  first  vertebra,  suffices  to  cause  even  a  large  mammal  to  fall  to  the 
ground  instantly.  Butchers  inflict  a  blow  on  the  nape  of  the  neck  to 
injure  the  vital  knot. 

COMPONENTS  OF  THE  CENTER. — The  center  of  respiration  in  the 
medulla  is  composed  of  an  inspiratory  center  and  an  expiratory  center. 

From  the  inspiratory  center  the  excitation  for  the  nerves,  and 
therefore  for  the  muscles  of  inspiration,  takes  its  departure  rhyth- 
mically. These  excitations  always  decussate  in  the  cervical  cord. 
The  inspiratory  excitation  reaches  the  center  by  means  of  the 
pneumogastric  nerves,  having  been  carried  along  their  sensory  pul- 
monary fibers.  The  excitation  is  originated  either  by  reason  of  an 
accumulation  of  C02  in  the  blood  or  the  absence  of  0.  On  the  con- 
trary, an  excess  of  oxygen  in  the  blood  abolishes  excitation  of  the 
inspiratory  center. 

The  expiratory  center,  on  the  other  hand,  gives  excitation  to  the 
nerves  and  muscles  of  forced  expiration  (normal  expiration  is  accom- 
plished by  reason  of  the  elasticity  of  the  thoracic  case). 

Experimentally  it  is  observed  that  exciting  the  vagus  nerves  or 
their  central  stumps  provokes  very  deep  inspirations  until  the  thorax 
stops  in  the  inspiratory  movement. 

Stimulating  the  superior  laryngeal  nerves  or  their  stumps 
provokes  violent  and  forced  expirations  until  the  thorax  stops  in  the 
expiratory  movement.  It  is  said  that  when  a  lesion  affects  the  bilateral 
respiratory  center  there  follows  immediate  suspension  of  breathing, 
and,  therefore,  death. 

The  medulla  oblongata  is  a  moderating  center  of  the  movements 
of  the  heart.  By  irritating  the  medulla  near  the  originating  nucleus 
of  the  vagus  nerve  there  is  caused  a  stoppage  of  the  cardiac  move- 
ments. The  heart  first  slackens  its  systole  and  afterward  stops  in 
diastole.  The  medulla  exercises  this  moderating  action  upon  the 
heart  through  the  vagus  nerve  as  a  medium.  Some  of  its  centrifugal 
fibers  put  themselves  in  relation  with  its  inhibitory  ganglia.  Hence,, 
moderation  and  suspension  of  the  heart  movements  are  obtained  by 
irritating  the  peripheral  stump  of  the  vagus  in  the  neck.  According 
to  Traube,  the  normal  stimulus,  capable  of  exciting  this  moderating 
action,  is  the  accumulation  of  C02  in  the  blood. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  461 

In  the  medulla  is  found  this  moderating  center,  which  is  antago- 
nistic to  that  other  center  seated  in  the  medulla  oblongata:  the 
accelerator  center  of  the  heart. 

The  medulla  contains  the  principal  vasomotor  center,  which  is  of 
the  utmost  importance  to  the  economy.  This  general  vasomotor 
center  in  the  medulla  may  become  stimulated  directly  from  the  l)rain. 
In  short,  an  emotion  or  irritation  to  the  cerebral  cortex  readily 
brings  on  ischemia  or  hypera3inia  either  in  the  skin  or  in  the  internal 
organs.  Thus,  there  may  be  pallor  from  fear  or  diarrhoea  from 
fright. 

This  organ  of  the  nervous  system  is  a  secretory  center  for  the 
saliva.  In  the  floor  of  the  fourth  ventricle  at  the  level  of  the  origin 
of  the  facial  nerve,  and  somewhat  posteriorly  to  it,  is  found  the 
originating  nucleus  of  the  fibers  of  the  intermediary  nerve  of  Wris- 
berg.  This,  through  the  chorda  tympani  of  the  facial  nerve,  is  car- 
ried to  the  submaxillary  gland.  Pricking  the  center  or  stimulating 
it  electrically  provokes  a  copious  secretion  of  saliva.  Certain  patho- 
logical lesions  may  produce  the  same  thing. 

GLUCOSE  SECRETION. — Concerning  this  secretion,  Bernard  dem- 
onstrated that  puncture  of  the  floor  of  the  fourth  ventricle  in  its 
median  line  above  the  sources  of  the  vagi  nerves  will  determine 
within  an  hour  the  condition  known  as  diabetes  mellitus:  glucose  in 
the  urine.  The  diabetes  ceases  if  the  liver  be  extirpated,  and  is  not 
produced  if  the  liver  has  been  previously  taken  away,  or  its  vessels 
have  previously  been  tied.  In  the  liver  of  animals  rendered  diabetic 
in  such  manner  there  is  found  an  intense  vasomotor  paralysis.  This 
appears  to  be  the  cause  of  the  increased  production  of  glucose. 

The  action  of  the  medulla  upon  the  liver  is  exercised  by  means 
of  the  spinal  cord  through  the  intervention  of  the  great  sympathetic. 

The  oblongata  centers  are:  (1)  respiratory.,  (2)  vasoconstrictor 
and  vasodilator,  (3)  cardio-inhibitory,  (4)  cardio-accelerator,  (5) 
diabetic  center,  (6)  vomiting  center,  (7)  deglutition,  (8)  salivation, 
and  (9)  mastication. 

ANATOMY  OF  THE  CEREBELLUM. 

The  cerebellum  is  situated  at  the  posterior  and  inferior  portion 
of  the  brain. 

It  is  bounded  anteriorly  by  the  cerebrum,  which  is  separated 
from  it  by  the  tentorium  of  the  cerebellum.  At  the  posterior  face 
of  the  cerebellum  are  the  pons  and  medulla  oblongata,  from  which 
structures  it  is  separated  by  the  fourth  ventricle.  The  cerebellum  is 


462  PHYSIOLOGY. 

entirely  covered  by  the  occipital  lobes  of  the  cerebrum  in  man,  but 
only  incompletely  so  in  monkeys.  It  is  united  by  the  cerebellar 
peduncles  to  the  cerebrum,  pons,  and  medulla. 

The  peduncles  are  six  in  number — three  on  each  side.  They  are 
known  as  the  superior,  middle,  and  inferior  cerebellar  peduncles. 

Surface  Form. — The  cerebellum  consists  of  a  median  lobe  (the 
vermis)  and  two  lateral  lobes  (the  cerebellar  hemispheres).  The  supe- 
rior vermiform  process  extends  from  the  notch  on  the  anterior  to  the 
one  on  the  posterior  border. 

The  under  surface  of  the  cerebellum  is  subdivided  into  two 
lateral  hemispheres  by  a  depression  (the  valley).  It  extends  from 
before  backward  in  the  median  line.  On  the  floor  of  the  median  lobe 
is  the  inferior  vermiform  process. 

Internal  Structure  of  the  Cerebellum, — The  cerebellum,  like  the 
spinal  cord,  is  composed  of  both  white  and  gray  substances.  The 
gray  is  the  most  abundant,  and  occupies  the  periphery  of  the  organ 
in  the  form  of  a  thin  layer  which  is  from  two  to  three  millimeters  in 
thickness. 

The  white  substance  is  placed  in  the  center  of  the  organ  and  is 
enveloped  in  all  of  its  parts  by  the  gray  matter.  The  white  represents 
nearly  one-third  of  the  whole  cerebellar  mass.  Its  consistency  is 
greater  than  that  of  the  gray  matter. 

The  central  nucleus  of  the  white  matter  sends  out  an  infinity  of 
arborescent  prolongations  which  terminate  in  the  cells  of  the  gray  sub- 
stance of  the  lamellae.  It  is  this  formation  which  the  student  knows 
under  the  name  of  arbor  vitce. 

Each  one  of  the  leaflike  divisions  of  the  white  arbor  vitse  forma- 
tion is  enveloped  by  a  very  thin  plate  of  yellowish  substance,  while 
above  this  is  the  cortical  gray  substance.  The  latter  sinks  into  the 
white  substance  at  the  level  of  the  grooves  which  separate  the  plates 
from  one  another. 

A  horizontal  section  of  the  cerebellum  shows  in  the  center  of  each 
half  of  the  organ  an  ovoid  body.  It  is  very  similar  to  the  olive  of 
the  bulb  in  size  and  structure.  This  is  the  corpus  dentatum. 

CORPUS  DENTATUM. — The  corpus  dentatum  is  formed  by  a  yellow 
layer  folded  upon  itself  in  the  form  of  a  purse  which  opens  in  front. 
Within  the  interior  of  this  purse  is  found  the  tissue  proper  of  the 
corpus  dentatum.  It  is  formed  of  a  matter  which  seems  to  be  a 
mixture  of  the  white  and  gray  substances. 

Under  the  name  of  accessory  nucleus  denlatus  Meynert  has  de- 
scribed two  small  leaves  of  gray  substance  located  in  front  and  inward 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


463 


from  the  corpus  dentatum.  They  are  the  nucleus  globosus  and  nucleus 
fastigii.  Stilling  has  discovered  two  clear  gray  nuclei  at  the  lower 
border  of  the  vermis  near  the  median  line  and  roof  of  the  fourth 
ventricle.  He  calls  them  the  nuclei  emboliformes.  Part  of  the  fibers 
of  the  inferior  cerebellar  peduncles  end  within  these  nuclei. 

Hence,  there  are  here  four  gray  nuclei:  dentate,  globosus,  fas- 
tigii, and  emboliformes.  The  last  three  are  in  pairs,  but  the  dentate 
is  single. 


Scm 


Cdc. 


Fig.  110.— Horizontal  Section  through  the  Cerebellum.     (After  B.  STILLING.) 

The  section  passes  through  the  region  under  the  corpora  quadrigemina 
(T),  then  through  the  anterior  cerebellar  peduncle  (R),  and  between  these 
through  the  lingula  (A).  Above  this  lies  the  nucleus  tegmenti,  nucleus 
fastigii  (m),  to  the  left  of  the  nucleus  globosus  (Ng),  the  embolus  (Emb), 
and  still  farther  to  the  side  within  the  hemisphere  the  corpus  dentatum 
(Cdc). 

The  central  white  substance  passes  toward  the  lateral  angles  of  the 
sinus  rhomboideus  in  three  prolongations  on  each  side.  They  are  the 
cerebellar  peduncles. 

The  superior  cerebellar  peduncles  go  forward,  pass  under  the  cor- 
pora quadrigemina,  where  they  decussate  with  one  another  in  the 
upper  level  of  the  cerebral  peduncles.  They  end  in  the  optic  thalamus 
and  cortex  of  the  brain. 

The  middle  cerebral  peduncles  pass  forward  and  inward  to  form 
the  superficial  annular  fibers  of  the  pons.  These  fibers  form  a  true 


464  PHYSIOLOGY. 

commissure  between  the  two  hemispheres  of  the  cerebellum;  other 
fibers  decussate  in  the  pons  to  terminate  in  the  islands  of  gray  sub- 
stance ;  a  last  category  ascends  into  the  brain  after  decussating  in  the 
pons  Varolii. 

The  inferior  cerebellar  peduncles  (corpus  restiformis)  pass  down- 
ward and  inward  to  the  level  of  the  medulla,  where  the  fibers  which 
form  them  separate  into  three  groups:  the  first  form  the  external 
arcuate  fibers  of  the  medulla;  the  second  are  thrown  into  the  post-, 
pyramidal  bodies  (nuclei  of  Groll  and  Burdach)  ;  and  the  third  are 
prolonged  directly  into  the  cord  under  the  name  of  direct  cerebellar 
tract. 

The  cortex  of  the  cerebellum  is  divided  into  two  layers:  the 
external  layer,  or  molecular  layer;  and  the  internal  granular  layer, 
the  rust-colored  layer,  or  nuclear  layer.  The  external  layer  is  made 
up  of  two  kinds  of  cells :  star-shaped  and  basket  cells.  The  neuraxons 
of  the  stellate  cells  enter  the  upper  part  of  the  molecular,  or  external, 
layer,  forming  a  network  of  fibers.  The  basket  cells  have  their  den- 
drons  extending  into  the  inner  part  of  the  molecular  layer,  while  their 
neuraxons  arborize  in  a  tuftlike  manner,  forming  a  "basket-work" 
about  the  cells  of  Purkinje.  The  internal  layer  is  made  up  of  multi- 
polar  cells  whose  neuraxons  form  the  horizontal  fibers  in  the  external, 
or  molecular,  layer.  These  horizontal  fibers  divide  in  a  T-shaped 
manner,  arborizing  about  the  dendrons  of  the  cells  of  Purkinje. 

In  the  granular  layer  are  relatively  large  cells  known  as  the  cells 
of  Golgi;  their  neuraxon  end  is  in  the  nuclear  layer,  while  their 
dendrons  lie  in  the  molecular  layer. 

Between  the  external  and  the  internal  layers  we  have  the  cells 
of  Purkinje,  which  are  supposed  to  be  the  cells  concerned  in  the  pres- 
ervation of  equilibrium.  The  dendrons  of  the  Purkinje  cells  occupy 
the  chief  part  of  the  external  layer,  and  have  little,  clublike  projections 
on  them.  The  neuraxons  of  the  Purkinje  cells  go  into  the  internal 
layer,  enter  the  external  layer,  and  arborize  about  the  dendrons  of  the 
cells  of  the  latter  layer. 

From  the  white  matter  come  fibers,  perhaps  from  the  spinal  cord, 
which  on  entering  the  granular  and  molecular  layers  have  at  their 
terminations  irregular  thickenings;  hence  called  moss-fibers  by  Cajal, 
who  believes  that  they  conduct  impulses  to  the  granular  cells. 

Another  kind  of  fiber  from  the  white  matter,  perhaps  from  the 
spinal  cord,  goes  through  the  granular  layer  into  the  molecular  layer, 
and,  like  a  climbing  plant,  clings  around  the  dendrons  of  the  cells  of 
Purkinje,  and  is  called  the  tendril  fiber. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          465 

Foster  holds  that  impulses  from  the  spinal  cord  or  other  parts 
pass  along  the  tendril  fibers  to  the  dendrons  of  the  Purkinje  cells  and 
by  its  neuraxons  from  the  cerebellum  to  other  parts,  or  other  impulses 
ma}'  be  caused  by  the  moss-fibers,  which  would  go  to  the  cells  of  the 
granular  layer.  From  here  the  impulse  would  be  carried  to  the  molec- 
ular layer  and  spread  along  the  bifurcating  fibrils  a  long  distance 
which  would  carry  them  to  the  dendrons  of  Purkinje  cells.  At  the 
same  time  the  arborizations  of  the  just-mentioned  bifurcating  fibrils 
running  in  longitudinal  directions  about  the  basket  cells  would  affect 
the  Purkinje  cells  in  an  indirect  manner,  and,  since  the  neuraxon  of 
each  basket  cell  bears  baskets  for  several  Purkinje  cells,  a  number  of 
these  Purkinje  cells  would  be  "associated"  in  the  same  event. 

The  cerebellum  has  a  threefold  grasp  on  the  cerebro-spinal  axis : 
1.  By  the  direct  cerebellar  tract  and  the  tract  of  Marchi  and  Loewen- 
thal;  by  the  restiform  bodies  and  inferior  cerebellar  peduncles.  2. 
By  the  middle  cerebellar  peduncles  connecting  the  nuclei  of  the  pons 
and  indirectly  by  these  nuclei  with  the  frontal  lobes.  3.  By  the 
superior  cerebellar  peduncles  where  the  corpus  dentatum  is  connected 
with  the  red  nucleus  and  where  the  cerebellum  is  connected  with  the 
nuclei  of  the  optic  thalamus,  and  through  new  neuraxons  of  the  optic 
thalamus  to  the  parietal,  ascending  frontal,  and  ascending  parietal 
of  the  opposite  side.  In  the  red  nucleus  we  have  a  point  of  union 
for  impulses  from  the  cerebellum  on  one  side,  and,  on  the  other  side, 
from  the  cerebrum. 

PHYSIOLOGY  OF  THE  CEREBELLUM  AND  MESENCEPHALON. 

Cerebellum. — Mechanical  irritation  applied  to  the  cortical  sub- 
stance of  the  cerebellum  does  not  cause  the  animal  to  cry  out  nor  are 
contractions  of  his  members  provoked.  Even  a  prick  or  a  wound  that 
is  not  very  deep  in  the  cerebellar  cortex  does  not  cause  any  noticeable 
or  constant  disturbances,  particularly  in  movements.  Most  often  the 
only  movements  are  those  of  the  ocular  globes. 

However,  a  deep  lesion  of  the  cerebellum — a  large  compression, 
a  tumor,  haemorrhage,  the  removal  of  all  or  a  large  portion  of  the 
cerebellum — determines  a  peculiar  ataxia  which  shows  the  loss  of 
equilibration.  The  animal,  desiring  to  move,  shows  great  uncertainty, 
irregularity,  and  want  of  co-ordination  of  movement.  Often  when  it 
wishes  to  take  some  steps,  it  falls  backward,  slipping  with  the  feet 
foremost. 

The  experiment  succeeds  best  in  birds.  After  removal  of  the 
cerebellum  they  can  no  longer  keep  their  balance.  This  is  known  as 

30 


466  PHYSIOLOGY. 

cerebellar  tottering.  Sometimes  after  several  efforts  they  succeed  in 
remaining  upon  their  feet  for  a  little  while,  but  they  soon  fall  and 
always  in  a  particular  manner.  They  slip  either  with  the  feet  spread 
wide  apart  laterally,,  so  as  to  touch  the  ground  with  the  breast,  or  else, 
slipping  with  the  legs  extended  forward,  they  support  themselves  with 
the  wings  behind.  The  head  is  folded  with  more  or  less  twisting  upon 
the  back.  When  these  animals  continue  to  live  for  some  time  with 
such  a  lesion,  they  end  by  presenting  characteristic  obstructions  with 
the  feet,  especially  in  the  disposal  of  the  toes. 

A  man  with  deep  lesions  of  the  cerebellum  has  very  noticeably 
disordered  movements  in  walking  and  standing  erect.  He  cannot  bal- 
ance himself  well.  While  walking  he  appears  like  one  who  is  drunk. 
He  suffers  intense  vertigo,  with  loss  of  balance,  which  renders  all  of  his 
movements  ataxic.  This  is  especially  so  of  motions  of  locomotion. 


Fig.  111.— Effects  of  Removal  of  Cerebellum.     (DALTON.) 

From  this  it  would  seem  that  the  cerebellum  is  the  center  of  the 
co-ordination  of  movements.  With  the  cerebellum  destroyed,  the  ani- 
mal can  no  longer  balance  itself.  Atrophy  of  one  cerebellar  hemi- 
sphere follows  atrophy  of  the  opposite  cerebral  hemisphere,  showing 
a  close  relation  between  them. 

The  function  of  equilibration  is  regulated  by  the  cerebellum, 
which  receives  afferent  impulses  as  follows : — 

1.  Tactile  impressions  by  the  posterior  columns  to  the  nuclei  of 
Goll  and  Burdach  and  from  them  by  the  restiform  body  to  the  cere- 
bellum. To  prove  that  tactile  impressions  are  necessary  to  co-ordina- 
tion it  is  simply  necessary  to  remove  the  skin  from  a  frog,  when  it 
will  not  be  able  to  leap,  swim,  or  resume  its  natural  position  when 
placed  on  its  back.  In  locomotor  ataxia  where  we  have  a  sclerosis 
of  the  posterior  columns  there  is  great  difficulty  in  walking. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 

2.  Visual  impressions  by  optic  nerve  conveyed  by  the  superior 
cerebellar  peduncle.     Ataxies  are  able  to  walk  much  better  when  they 
fix  their  eyes  on  the  ground,  and  when  they  close  their  eyes  walking 
becomes  impossible. 

3.  Muscular-sense  impulse  through  the  direct  cerebellar  tract  by 
the  restiform  body  to  the  vermis. 

4.  Impressions  from  the  semicircular  canals,  which  will  be  con- 
sidered under  the  "Semicircular  Canals."     Here  the  vestibular  nerve 
carries  impressions  from  the  semicircular  canals  by  the  restiform  body 
to  the  nucleus  fastigii  and  nucleus  globosus  of  the  cerebellum. 

The  motor  tract  from  the  cerebellum  is  possibly  the  tract  of 
Loewenthal  and  Marchi,  which  arises  in  the  cerebellum  and  runs  down 
by  the  inferior  cerebellar  peduncle  to  the  antero-lateral  column. 

In  addition  to  the  tottering  walk  and  vertigo,,  deep  lesions  of  the 
cerebellum  in  man  produce  a  tendency  to  vomiting.  This  is  probably 
due  to  the  irritation  which  spreads  to  the  center  of  the  origin  of  the 
vagus  nerve  in  the  underlying  medulla  oblongata.  Sometimes  there 
is  found  a  disposition  to  dyspnoea  and  syncope  for  the  same  reason. 
Frequently  there  are  changes  in  the  organ  of  sight,  as  amaurosis, 
strabismus,  and  astigmatism. 

MIDDLE  PEDUNCLES. — Deep  lesion  of  the  middle  peduncles  of 
the  cerebellum  (those  which  pass  to  the  pons  Varolii),  if  made  upon 
one  side  only  produces  in  the  animal  a  tendency  to  turn  or  rotate 
upon  the  principal  axis  of  its  body.  If  the  lesion  occur  in  the  pos- 
terior part  of  the  peduncle  the  rotation  is  toward  the  side  where  the 
peduncle  is  cut.  The  animal  may  make  as  many  as  sixty  or  more 
revolutions  per  minute.  The  rotation  will  be  toward  the  opposite  side 
when  the  anterior  portion  of  the  peduncle  has  been  injured.  This 
rotation  is  explained  by  Schiff,  who  admits  paralysis  of  the  rotary 
muscles  of  the  head  and  one  side  of  the  spinal  column. 

Cutting  the  middle  cerebellar  peduncle  brings  on  internal  strabis- 
mus in  the  eye  on  the  side' operated  upon,  but  external  superior  stra- 
bismus in  the  eye  upon  the  opposite  side. 

Lesion  of  the  inferior  peduncle  of  the  cerebellum  or  of  the  bulb 
becomes  painful.  Also  the  animal  falls  upon  the  opposite  side  and  is 
unable  to  keep  itself  erect.  The  animal's  body  is  presented  curved  in 
the  form  of  an  arch  toward  the  side  of  the  lesion. 

Lesion  of  the  superior  peduncle  does  not  give  characteristic  and 
precise  phenomena. 

The  Pons. — The  pons  represents  a  crossed  way  of  conductibility 
between  the  periphery  of  the  body  and  the  brain,  and  vice  versa.  Be- 


468  PHYSIOLOGY. 

sides,  it  is  a  co-ordinating  center  of  the  actions  that  pass  through. 
The  pons  Varolii,  at  its  anterior  surface,  shows  itself  to  be  but  very 
little  or  not  at  all  irritable.  Posteriorly,  there  are  signs  of  great 
pain  and  agitation  in  the  animal  under  stimulation.  Deep  irritation 
causes  convulsions  and  pains  according  to  the  kind  of  fibers  irritated. 
The  facial  nerve  is  often  found  paralyzed  upon  the  same  side  as  the 
lesion  and  so  opposite  to  the  paralysis  of  the  members  and  trunk. 
This  condition  is  spoken  of  as  alternate  hemiplegia. 

The  pons  Varolii  is  the  center  of  epileptiform  convulsions.  Deep 
irritation  with  electricity  to  the  substance  of  the  pons  causes  general 
epileptiform  movements  in  the  animal.  Nothnagel,  by  irritating  with 
the  needle,  has  defined  the  limits  of  the  spasmodic  territory,  or  region 
of  cramps.  This  convulsive  center  is  irritated  by  excess  of  C02  in 
the  blood,  or  else  by  absence  of  the  proper  proportion  of  oxygen.  Oil 
of  absinthe  is  capable  of  irritating  this  center.  * 

Cerebral  Peduncles. — The  cerebral  peduncles  contain  all  of  the 
fibers  of  sensation  and  motion  in  the  body  and  direct  them  (except 
a  few)  toward  the  large  ganglia  at  the  base  of  the  brain.  Stimulation 
of  a  peduncle  produces  pain  and  contractions  in  the  opposite  half  of 
the  body;  section  or  deep  lesion  from  disease  produces  paralysis  and 
anaesthesia  in  the  opposite  half  of  the  body. 

The  cerebral  peduncles,  therefore,  carry:  (1)  the  voluntary  exci- 
tations to  the  nerves  of  motion  and  so  to  the  muscles;  and  (2)  the 
sensitive  impressions  made  upon  the  peripheral  extremities  of  the 
centripetal  nerves  up  to  the  brain. 

I, have  found  in  the  cat  that  mechanical  irritation  of  the  locus 
niger  will  cause  the  bladder  to  contract,  indicating  a  high  detrusor 
center.  Mechanical  irritation  to  any  part  of  brain  in  front  of  this 
point  has  no  effect  on  the  bladder. 

In  the  greater  number  of  unilateral  lesions  of  the  cerebral  pe- 
duncle the  so-called  movement  in  a  circle  is  observed.  That  is,  the 
animal  walks  or  flies,  but  always  follows  the  curve  of  circumference. 
This  is  usually  to  the  side  opposite  the  lesion. 

Corpora  Quadrigemina. — In  man  atrophy  of  the  opposite  anterior 
quadrigeminal  body  follows  removal  of  an  eye.  The  anterior  quad- 
rigemina  are  also  centers  for  the  reflex  movements  of  the  iris.  As  the 
student  already  knows,  the  pupil  contracts  in  the  presence  of  strong 
light,  but  enlarges  in  a  faint  light  or  darkness.  If  the  anterior  quad- 
rigeminal bodies  be  destroyed,  the  pupil  remains  immovable  and 
dilated  even  in  the  presence  of  a  strong  light. 

Besides  these  functions  for  the  eye,  the  quadrigeminal  bodies  are 


ANATOMY  AXD  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          459 

believed  to  serve  other  reflex  actions.  The  posterior  quadrigeminal 
bodies  are  pathways  of  auditory  fibers.  They  are  also  regarded  as 
centers  of  co-ordination  of  movements;  their  destruction  is  accom- 
panied by  disturbances  of  mobility. 

PHYSIOLOGY  OF  THE  OPTIC  THALAMI  AND  STRIATED  BODIES. 

The  optic  thalami,  if  deeply  stimulated  or  injured,  appear  to  be 
but  slightly  irritable  and  little  or  not  at  all  sensitive.  The  animal 
has  shocks  or  shrinkings,  but  does  not  cry  out.  A  deep  lesion,  made 
in  the  posterior  third  of  the  optic  thalamus,  determines  in  the  animal 
movements  in  a  circle  from  the  injured  side  toward  the  sound  side. 
If,  however,  the  lesion  be  made  in  the  anterior  part  of  the  thalamus, 
the  circular  movement  is  reversed. 

Opinion  seems  to  be  divided  as  to  the  effect  produced  by  lesion 
of  the  optic  thalamus  upon  the  visual  function.  It  is  concluded,  how- 
ever, that  the  surface  of  the  thalamus  (in  conjunction  with  the  corpora 
quadrigemina)  is  connected  with  sight. 

In  addition  to  the  functions  just  mentioned,  the  optic  thalami 
have  an  influence  upon  the  sensibility  of  the  opposite  side  of  the  body. 
That  is,  not  conscious  sensibility,  but  that  tactile  and  muscular  sensi- 
bility necessary  for  the  execution  of  extended  and  co-ordinate  move- 
ments. This  is  especially  so  for  locomotion  without  the  aid  of  the 
will.  These  movements,  then,  are  none  else  than  reflex.  They  respond 
to  the  impressions  made  upon  the  sensory  surface  of  the  body  and 
reflected  in  the  large,  excitomotor  centers,  viz.,  the  thalami.  The 
thalami  are  relay  centers  for  the  sensory  tract. 

Thus,  while  a  normal  individual  walks  along  a  clear  street,  per- 
il aps  he  thinks  of  his  movements  but  once.  During  that  short  time 
his  will  directs  his  volitional  impulses;  the  rest  of  his  walk,  on  the 
contrary,  is  executed  almost  automatically.  In  this  case  the  excita- 
tions take  their  departure  from  impressions  upon  the  body  by  the 
ground,  space,  weight  of  the  body,  etc.  These  impressions  are  all 
summed  up  in  the  optic  thalami,  from  which  they  return,  co-ordi- 
nated, along  the  nerves  of  motion. 

When  the  striated  bodies  are  irritated  they  do  not  provoke  any 
signs  of  pain.  Though  the  animal  remains  relatively  quiet  under 
ablation  of  the  hemispheres,  yet  it  is  seized  with  violent  and  con- 
vulsive contractions  in  the  opposite  half  of  the  body  when  the  striated 
body  is  hardly  reached.  This  response  is  especially  marked  in  the 
lenticulo-striate  part  of  the  internal  capsule.  By  stimulating  a  stri- 


470 


PHYSIOLOGY. 


ated  body  with  electricity,  tetanus  in  the  opposite  half  of  the  body 
has  been  obtained.  The  corpora  striata  are  motor  relay  centers.  They 
also  contain  a  thermogenic  center. 

EXPERIMENTAL  PHYSIOLOGY  OF  CEREBRAL  HEMISPHERES. 

There  are  two  great  means  that  experimental  physiology  has  at 
its  disposal,  viz. :  stimulation  (electrical,  mechanical,  chemical,  and 
thermal)  and  removal.  These  are  likewise  applied  to  the  most  im- 
portant and  noble  part  of  the  nervous  apparatus:  the  cerebral  hemi- 
spheres. The  experimental  results  are  then  compared  with  those 


Fig.  112. — Left  Cerebral  Hemisphere  in  Man,  Showing  Areas  of  Localization. 

observed  in  clinics  from  pathological  lesions  located  and  circumscribed 
in  various  points  of  the  same  hemispheres. 

Some  years  ago  all  physiologists  admitted  the  complete  inexcita- 
bility  of  the  cortical  substance  of  the  cerebral  hemispheres.  Accord- 
ing to  the  view  then  held,  mechanical,  thermal,  chemical,  and  electrical 
irritation  of  the  convolutions  did  not  determine  phenomena  of  any 
kind. 

Later,  however,  it  was  demonstrated  that  very  slight  electrical 
currents  applied  to  the  cerebral  convolutions  in  dogs  determined  vari- 
ous movements  in  the  head,  limbs,  eyes,  etc.  By  this  means  the 
operator  can  cause  the  execution  of  various  movements  to  suit  his 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


471 


will,  as,  for  example,  closing  the  fist,  extending  the  arm,  moving  the 
leg,  eyes,  face  muscles,  etc.  These  results  were  best  demonstrated  in 
experiments  upon  apes.  By  experiments  along  this  line  it  has  become 
feasible  to  fix  the  seat  of  various  cortical  motor  centers  of  the  brain. 
In  man  himself  experiments  with  electricity  have  been  made  upon  the 
convolutions  exposed  from  various  causes. 


w 

Cerebellum. 


Fig.  113. — Left  Cerebral  Hemisphere  in  Man,  Showing  Areas  of  Localization. 

Motor  and  Sensory  Centers. 

The  motor  centers  are  located  in  the  ascending  frontal,  ascend- 
ing parietal,  and  paracentral  convolutions.  The  foot  of  the  third 
left  frontal  convolution  contains  the  center  of  speech. 

The  tactile  centers  have  been  located  by  the  neurologist  in  the 
same  area  as  the  motor  centers.  The  physiologist  places  them  in 
the  gyrus  fornicatus. 

The  visual  area  corresponds  to  the  occipital  lobe.  Its  unilateral 
destruction  produces  bilateral,  but  passing,  hemianopsia.  Bilateral 


472  PHYSIOLOGY. 

destruction  produces  complete  blindness  at  first,  but  later  only  ambly- 
opia  with  impossibility  of  distinguishing  objects.  Excitation  of  this 
region  on  one  side  produces  a  sidewise  movement  of  the  eye  toward  the 
side  of  the  lesion,  with  a  contraction  of  the  pupils,  and  known  as 
conjugate  deviation.  Lesions  of  the  cuneus  are  usually  the  cause  of 
hemianopsia,  or  half-blindness. 

The  auditory  area  is  found  in  the  superior  temporo-sphenoidal 
region.  Its  unilateral  removal  causes  temporary  deafness  on  the  oppo- 
site side.  Bilateral  removal  causes  complete  deafness  on  both  sides. 
Excitation  of  this  region  determines  movements  in  the  eyes,  pupils, 
head,  and  ears  as  if  the  animal  had  heard  a  loud  sound. 

The  centers  for  taste  and  smell  are  localized  in  the  uncus. 

The  motor  speech  center  is  located  in  the  posterior  part  of  the 
inferior  left  frontal  gyrus  and  the  island  of  Eeil.  When  this  center 
is  destroyed  there  is  produced  a  defect  in  speech  known  as  aphasia, 
which  is  an  inability  to  give  correct  utterance  to  thought.  Another 
condition — inability  correctly  to  write  one's  thoughts,  and  often  asso- 
ciated with  aphasia — is  known  as  agraphia.  A  lesion  of  the  base  of  the 
second  left  frontal  convolution  is  probably  the  motor  writing  center. 
The  tactile  area,  according  to  the  physiologists,  is  found  in  the  gyrus 
fornicatus;  according  to  the  neurologists,  in  the  ascending  parietal 
and  parietal  convolutions. 

To  conclude,  it  may  be  said  that  the  normal,  physiological  sig- 
nificance of  these  cortical  centers  cannot  be  other  than  that  they  are 
primitive  motor  and  sensory  centers.  The  motor  centers  may  be  con- 
sidered as  the  origin  of  primitive  impulses  which  produce  voluntary 
movements.  They  are,  then,  psychical  motor  centers  or  even  centers  of 
motor  ideation. 

The  sensory  areas  would  be  centers  of  conscious  sensation,,  or  cen- 
ters of  perception.  These  various  centers,  by  means  of  definite  bundles 
of  nervous  fibers,  are  in  relation  with  particular  muscular  groups  or 
else  with  special  organs  and  sensory  regions. 

PHENOMENA  FOLLOWING  THE  DESTRUCTION  OF  ONE  OR  BOTH 
OF  THE  CEREBRAL  HEMISPHERES. 

Ablation  of  the  cerebral  hemispheres  is  generally  performed  in 
frogs  or  fowls,  who  seem  to  endure  the  operation  sufficiently  well. 
Mammals  easily  succumb. 

The  skin  of  the  head  being  cut  and  the  thin  cap  of  the  skull 
removed,  the  brain  is  reached.  The  incision  of  the  meninges  is  pain- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          473 

fill,  but,  after  gradually  removing  the  mass  of  the  hemispheres  from 
above  downward,  the  bird  shows  itself  indifferent.  In  fact,  it  be- 
comes more  stupid  and  apathetic  the  more  of  the  cerebral  tissue  is 
removed.  The  removal  of  the  hemispheres  completed  without  injur- 
ing the  peduncular  system,  with  its  ganglia,  and  the  hemorrhage 
stopped  as  well  as  possible,  the  bird  remains  in  a  sleepy  state.  It 
has  a  tendency  to  bury  the  head  and  close  its  eyes ;  it  breathes  slowly, 
but  does  not  walk  away. 

Under  stimulation  the  bird  reopens  its  eyes,  raises  the  head,  takes 
a  few  steps,  then  suddenly  returns  to  its  former  position. 

The  bird,  having  recovered  from  its  traumatism,  the  following 
phenomena  are  observed  within  a  few  days:  The  bird  has  become 
an  automaton.  It  does  not  eat,  so  that  it  becomes  necessary  to  put  the 
food  into  its  mouth.  It  moves  not  at  all  of  its  own  volition ;  if  pur- 


Fig.  114.— Effects  of  Ablation  of  Cerebrum.     (DALTON.) 

sued  it  takes  some  steps;  its  pupil  contracts  under  the  influence  of 
the  light,  cries  or  tries  to  flee  when  the  skin  is  irritated.  It  is  startled 
by  loud  noises.  For  the  rest  there  are  no  longer  voluntary  movements, 
and  the  few  movements  observed  are  aroused  by  external  excitement, 
or  some  internal  need.  The  movements  are  rubbing  the  skin  with 
the  beak,  scratching  the  head  with  the  foot,  etc. 

The  vegetative  functions  (once  that  care  is  taken  to  nourish  the 
birds  and  clean  them)  are  performed  without  disturbances.  If  the 
bird  lives  for  some  time  it  shows  a  general  deposit  of  fat.  The  skin 
and  muscles  in  particular  are  seen  to  be  infiltrated  with  adipose  tissue. 

In  these  birds  there  are  only  movements  of  a  reflex  nature. 

Sensibility  is  blunted  since  the  stimuli  are  not  able  to  reach  the 
cortical  centers.  Hence,  they  cannot  provoke  volitional  acts  in  them, 
as  Kiiss  says,  these  birds  live,  but  do  not  perceive;  they  hear,  but 
do  not  listen;  they  are  aware  of  stimuli  uDon  the  tongue,  but  do  not 
taste  them.  They  are  just  as  a  human  being  who  is  asleep  or  absorbed 


474  PHYSIOLOGY. 

in  contemplation.     He  may  drive  a  fly  from  the  face  without  being 
conscious  of  it. 

When  but  one  cerebral  hemisphere  is  removed  without  in  the' 
least  injuring  the  other  and  the  animal  recovers,  it  does  not  show 
positive  disturbances  of  intelligence  or  conscious  sensibility  or  of 
voluntary  motion.  However,,  the  opposite  side  shows  weakness. 
Should  the  lesion  extend  to  the  underlying  basal  ganglia  or  to  the 
peduncular  system,  there  will  be  complete  hemiplegia  in  the  opposite 
side  of  the  body.  The  same  manifestations  are  observed  in  a  man 
who  has  lost  an  entire  hemisphere  from  a  wound  or  from  disease. 
There  is  no  positive  lesion  of  intelligence,  but  there  is  manifested  very 
marked  fatigue  from  intellectual  labors.  If  the  lesion  has  extended 
toward  the  peduncular  base  of  the  hemisphere,  there  is  hemiplegia  in 
the  opposite  side  of  the  body. 

The  crowbar  case  is  a  much-cited  instance.  A  workman  twenty- 
five  years  of  age  was  engaged  in  charging  a  blast  in  a  rock.  The 
instrument  he  used  was  a  sharp-pointed  bar,  forty  inches  long,  one 
and  one-fourth  inches  in  diameter  and  weighing  twelve  pounds.  The 
charge  was  suddenly  exploded,  driving  the  bar  so  that  it  entered  the 
man's  lower  jaw  and  came  out  at  the  top  of  the  head  close  to  the 
sagittal  suture  in  the  frontal  region.  It  fell  at  some  distance,  covered 
with  blood  and  brains.  For  the  moment  the  victim  remained  uncon- 
scious. An  hour  after  the  accident  he  walked  to  the  house  of  a  sur- 
geon, where  he  gave  an  intelligent  account  of  the  accident.  For  a 
long  time  his  life  was  despaired  of,  but  he  finally  recovered  to  live 
twelve  and  one-half  years  longer. 

It  may  be  concluded,  therefore,  that  one  cerebral  hemisphere  only 
is  sufficient  for  the  mobility  and  sensibility  of  the  two  sides  of  the  body, 
as  well  as  the  performance  of  psychical  functions.  The  individual 
with  one  hemisphere  destroyed  remains  like  one  who  has  lost  an  eye. 
That  is  to  say,  the  brain  continues  to  perform  its  functions,  animal  as 
well  as  psychical,  but  with  noticeable  weakness,  greater  effort,  and 
fatigue.  The  frontal  lobes  are  the  chief  seat  of  the  will,  memory,  and 
intellectual  functions. 

The  irritability  of  the  cerebral  cortex  may  be  diminished  or  ex- 
aggerated by  various  circumstances.  Thus,  opium,  ether,  chloroform, 
chloral,  the  bromides,  cold,  asphyxia,  etc.,  diminish  it.  Inflamma- 
tion, urea,  uric  acid,  atropine,  strychnine,  etc.,  increase  its  excitability. 

Action  of  Brain  Extracts. — In  1898  I  found  that  infusions  of 
dried  brain  reduced  the  heart's  frequency  and  the  arterial  tension. 
Section  of  the  vagus  or  its  paralysis  by  atropine  did  not  prevent  this 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.          475 

action.  Halliburton  did  not  obtain  the  same  results  after  the  use  of 
atropine,  but  my  experiments  have  been  confirmed  by  Swale  Vincent 
and  Sheen.  Quite  recently  Swale  Vincent  and  Cramer  have  found  two 
substances  in  brain,  both  depressing  the  heart  even  after  the  previous 
use  of  atropine.  They  also  obtained  another  substance  depressing  the 
circulation,  but  its  effects  are  abolished  by  atropine. 

THE  GREAT  SYMPATHETIC. 

The  great  sympathetic  is  composed  of  a  double  chain  of  ganglia, 
situated  at  the  sides  of  the  vertebral  column  upon  its  visceral  surface 
and  known  as  the  lateral  or  vertebral  ganglia.  This  chain  may  be 
divided  into  four  parts,  viz. :  cervical,  thoracic,  abdominal,  and  pelvic. 
In  addition  to  these  main  ganglia  others  are  found  either  along  the 
course  of  the  cranial  nerves  (submaxillary,  optic,  spheno-palatine, 
ciliary,  etc.)  or  interspersed  among  the  splanchnic  organs.  These 
latter  are  found  in  the  heart,  lungs,  mesentery,  the  intestines,  bladder, 
vessels,  etc.,  and  are  known  as  the  prevertebral  ganglia. 

The  ganglia  of  the  two  cords  of  the  sympathetic  are  in  relation 
with  the  cerebro-spinal  axis  by  means  of  the  communicating  branches. 
These  proceed  from  the  anterior  and  posterior  roots  of  the  spinal 
nerves.  They  are  constituted,  for  the  most  part,  of  delicate  medullary 
tubes :  centripetal  and  centrifugal.  They  come  from  the  mixed  nerves 
of  animal  life  to  enter  the  ganglia  and  so  put  themselves  in  relation 
with  the  ganglionic  cells.  From  these  cells,  then,  issue  bundles  of 
fibers  known  as  Remaps  gray  fibers.  These,  joined  to  the  medullary 
fibers  of  the  communicating  branches,  go  to  make  up  the  so-called 
plexuses  of  the  great  sympathetic  around  each  organ  of  the  neck, 
thorax,  abdomen,  and  pelvis,  consisting  of  the  prevertebral  ganglia. 
The  preganglionic  sympathetic  fibers  which  are  concerned  in  the  nerve- 
supply  of  vessels,  glands,  or  the  visceral  muscles  pass  through  the 
chain  of  lateral  or  vertebral  ganglia  to  end  in  some  of  the  prevertebral 
ganglia.  Here  they  arborize,  making  a  sort  of  contact.  From  the 
prevertebral  ganglia  run  fibers  to  the  tissues  concerned  and  these 
fibers  are  the  postganglionic  fibers. 

A  portion  of  the  fibers  issuing  from  the  ganglionic  cells  retrocede 
into  the  communicating  branches.  They  either  distribute  themselves 
to  the  mixed  spinal  nerves  or  else  penetrate  the  spinal  cord. 

The  plexuses  of  the  sympathetic  are  inseparable  companions  of 
the  arterial  branches;  their  centrifugal  branches  go  to  the  muscles 
with  smooth  fibers,  while  the  centripetal  branches  are  distributed, 
for  the  most  part,  to  the  mucous  membrane^. 


476  PHYSIOLOGY. 

The  cervical  part  of  the  great  sympathetic  is  composed  of  three 
ganglia  with  certain  vasomotor  branches  which  follow  some  of  the 
neighboring  large  vessels. 

The  thoracic  portion  is  composed  of  twelve  ganglia  upon  each 
side.  From  this  part  issues  the  cardiac  plexus.  The  inferior  thoracic 
ganglia  give  off  the  splanchnic  nerves,  which  are  distributed  to  the 
plexuses  of  the  abdominal  viscera.  Unlike  the  branches  of  the  sym- 
pathetic, they  are  white  and  hard,  like  the  spinal  branches. 

The  abdominal,  or  lumbar,  part  consists  of  four  ganglia  whose 
branches,  together  with  the  splanchnic  nerves,  branches  of  the  aortic 
plexus,  and  the  right  vagus  nerve  constitute  the  solar,  or  cosliac,  plexus. 

The  pelvic  portion  consists  of  five  or  six  ganglia,  including  the 
coccygeal  ganglion. 

As  regards  the  general  physiology  of  the  great  sympathetic,  it  can 
be  said  that  this  system  gives  to  the  mucous  membranes  and  the  in- 
nervated splanchnic  organs  an  obtuse  sensibility.  That  is,  a  sensibility 
which  does  not  make  the  individual  notice  the  normal  stimuli  (ali- 
ment, air,  blood,  liquids  of  secretion,  etc.),  but  purely  the  abnormal 
stimuli.  The  latter  produce  a  pain  which  is  dull,  not  very  well 
defined,  and  not  localized.  For  this  reason  it  is  called  general  sen- 
sibility. 

Furthermore,  the  sympathetic,  with  its  centrifugal  branches,  gives 
to  the  smooth  muscular  fibers  a  mobility:  that  is,  a  mobility  which 
never  comes  into  play  by  volitional  impulse.  It  is  always  aroused 
by  reflex  actions  which  give  reflex  phenomena.  Contraction  of  smooth 
muscles,  from  excitation  of  the  sympathetic,  requires  a  long  time  of 
latent  irritation;  it  is  established  slowly,  and  also  disappears  slowly. 
The  actions,  instead  of  being  instantaneous  and  intense,  become  rela- 
tively unconscious,  lasting,  and  weak. 

If  the  spinal  cord  be  wholly  destroyed,  stimulus  to  the  intestinal 
mucous  membrane  is  followed  by  peristalsis.  This  occurs  from  reflex 
action  in  the  cells  of  the  sympathetic  plexuses  existing  between  the 
layers  of  the  intestine  itself. 

Finally,  with  the  sympathetic  run  many  vasomotor,  secretory,  and 
trophic  nerves. 

LITERATURE  CONSULTED. 
Quain's  "Anatomy." 
Debierre,  "La  Moelle." 


CHAPTER  XV. 

SPECIAL   SENSES. 
TACTILE  SENSE. 

THE  organs  of  special  sense  constitute  the  peripheral  portion  of 
the  centripetal  part  of  the  nervous  system.  The  nervous  system  is 
open  to  receive  the  impressions  from  the  external  world  according 
to  the  nature  of  the  different  agents  which  must  impress  the  organs 
of  the  special  senses. 

The  various  kinds  of  sense-organs  have  each  a  different  con- 
struction. They  are  always  adapted  to  receive  an  impression  of  a 
given  agent.  Thus,,  the  eye  is  an  organ  that  is  particularly  adapted 
to  receive  impressions  from  rays  of  light;  the  ear  receives  sound- 
waves ;  the  skin  is  responsive  to  touch,  etc. 

Man  is  endowed  with  five  senses.  That  is,  he  possesses  five  kinds 
of  organs  which  are  destined  to  give  him  notice  of  the  impressions 
upon  his  nervous  system  from  five  different  agents.  To  these  agents 
man  has  assigned  special  names  which  recall  their  relations  to  the 
organs  of  sense,  and  without  which  they  could  not  be  conceived  of. 
These  agents,  with  the  corresponding  organs  of  sense,  are  (1)  contact, 
which  is  perceived  through  the  sense  of  touch,  whose  highest  devel- 
opment is  in  the  skin;  (2)  taste,  a  modification  of  touch  is  perceived 
through  the  sense  of  taste  embodied  in  the  tongue ;  (3)  odor  is  recog- 
nized through  the  sense  of  smell  as  located  in  the  nose;  (4)  sound- 
waves are  made  known  to  the  economy  through  the  sense  of  hearing, 
whose  peripheral  organ  is  the  ear;  and  (5)  light  is  perceived  through 
sight  by  reason  of  the  response  produced  in  the  eye  from  the  excita- 
tion of  rays  of  light. 

The  various  peripheral  organs  of  special  sense  respond  best  and 
give  the  clearest  centripetal  impulses  when  they  are  stimulated  by 
excitations  peculiarly  their  own.  Thus,  waves  of  light  are  best  re- 
ceived by  the  eye,  sound-waves  by  the  ear,  and  so  on.  However,  the 
fact  must  not  be  lost  sight  of  that  any  other  excitation  than  the  proper 
one  acting  upon  these  organs  will  always  be  perceived  by  the  indi- 
vidual in  the  same  way  as  an  appropriate  impression.  An  induction 
current  upon  the  skin  will  produce  unpleasant  tactile  sensations. 

(477) 


478  PHYSIOLOGY. 

Upon  the  eye  it  provokes  luminous  sensations,  upon  the  ear  noise 
sensations,  and  upon  the  tongue  there  is  produced  a  sensation  of 
taste.  Yet  in  each  case  the  stimulus  is  always  the  same. 

In  order  that  the  impressions  caused  by  the  external  excitants 
may  be  able  to  reach  the  consciousness  of  the  individual,  it  becomes 
necessary  that  each  organ  of  sense  be  furnished  with  centripetal 
nerves.  These  are  in  direct  anatomical  relation  with  the  central 
nervous  system.  By  means  of  these  nerves  the  cortical  portion  of  the 
cerebrum,  endowed  with  consciousness,  perceives  the  impressions  com- 
ing from  the  external  world.  These  are  the  so-called  special,  external, 
and  objective  sensations. 

Among  the  parts  furnished  with  nerves  of  general  sensibility  are 
the  mucous  membrane  of  the  digestive,  respiratory,  and  genito-urinary 
tracts,  and  the  skeletal  muscles.  In  the  digestive  tract,  the  mouth, 
pharynx,  and  anus  are  endowed  with  tactile  nerves;  the  rest  of  the 
tract  is  furnished  with  nerves  of  general  sensibility.  The  mucous 
membrane  of  the  oesophagus  gives  us  the  sensation  of  thirst,  the 
gastric  mucous  membrane  the  sensation  of  hunger  and  satiety,  while 
the  rectal  membrane  notifies  the  individual  of  the  need  of  defecation. 

Pulmonary  tissue  in  itself  has  but  very  little  sensibility;  but  ab- 
normal irritations  cause  cough  and  painful  sensations.  The  pleura, 
when  invaded  by  disease,  produces  very  painful  sensations. 

The  genito-urinary  membrane,  besides  its  exquisite  tactile  sensi- 
bility, is  also  the  seat  of  general  sensibility  that  is  doubly  modified : 
in  the  need  of  urination  and  the  sexual  sense.  The  kidneys,  ureters, 
testes,  JFallopian  tubes,  and  the  uterus  are  endowed  only  with  nerves 
of  general  sensibility. 

The  skeletal  muscles  are  furnished  with  the  so-called  muscular 
sense.  This  is  none  other  than  general  sensibility.  It  conveys  disa- 
greeable sensations  only  when  the  stimulus  becomes  intense  or  ab- 
normal. When  a  muscle  is  irritated  or  lacerated  it  gives  rise  to  pain. 
Fatigue  is  generally  localized  as  an  unpleasant  sensation  in  the 
muscles.  A  proof  of  muscular  sense  is  the  employment  of  enough 
force  to  overcome  resistance.  Consciousness  is  a  large  factor  in  this 
last  function,  for  by  it  the  individual  judges  the  amount  of  resistance. 
He  then  voluntarily  regulates  the  amount  of  muscular  effort. 

It  is  by  the  sum  of  all  the  sensations  from  the  nerves  of  general 
sensibility,  as  well  as  the  sensation  produced  by  muscular  movement, 
that  individuals  feel  that  they  exist.  With  these  data  the  individual 
recognizes  the  state  of  different  parts  of  his  body,  whether  in  repose 
or  activitv. 


TACTILE  SENSE.  479 

Laws  of  Sensations. — Special  sensations  are  subject  to  the  fol- 
lowing laws : — 

1.  For  every  nerve  of  sense  there  is  a  nominal  degree  or  limit  of 
stimulus  which  gives  no  sensation  whatever.     There  is  also  a  max- 
imum degree  beyond  which  an  increase  of  the  intensity  of  the  stim- 
ulus brings  on  pain  or  an  unpleasant  sensation. 

2.  The  minimum  limit  varies  for  the  separate  sensations,  or, 
rather,  the  single  specific  agents.     Thus,  the  minimum  for  excitation 
of  touch  is  a  pressure  of  0.002  milligram;    for  temperature,   1/8° 
C. ;   for  sensation  of  movement,  a  shortening  to  the  extent  of  0.044 
millimeter  of  the  internal  rectus  of  the  eye;    for  hearing,  the  noise 
made  by  a  ball  of  pith  1  milligram  in  weight  falling  1  millimeter  in 
height  upon  a  glass  plate  heard  at  a  distance  of  91  millimeters  from 
the  ear ;   for  sight,  an  intensity  of  light  about  one  three-hundredth  as 
strong  as  that  of  the  full  moon. 

3.  The  intensity  of  the  sensation  is  proportional  to  the  intensity 
of  the  stimulus  and  the  degree  of  irritability  of  the  nerve  at  the 
moment  of  excitation.    As  the  strength  of  the  stimulus  increases,  so 
do   the  sensations.     But  the   sensations   increase   equally   when   the 
strength   of   the   stimulus   increases   in   relative  proportions.     Thus, 
small  noises  will  be  distinguished  in  the  silence,  not  in  the  midst  of 
loud  noises ;  a  slight  difference  will  be  noticed  between  small  weights, 
not  between  heavy  ones.     A  burning  candle  in  the  daytime  makes 
little  impression. 

4.  Sensations   do  not  increase  in  the  same  proportion  as  the 
stimulus.     If  the  stimulus  increase  in  geometrical  progression,  then 
the  sensation  increases  in  simple  arithmetical  progression.     Rather, 
it  increases  as  the  logarithm  of  the  strength  of  the  stimulus.     (This  is 
Fechner's  psycho-physical  law.) 

5.  For  the  single,  specific  sense  apparatuses,  wherever  a  stimulus 
takes  place,  whether  at  the  peripheral  terminations  of  a  nerve  or  in 
its  course,  or  at  its  central  point,  the  individual  always  localizes  with 
his  perception  the  stimulus  at  the  place  where  the  normal  stimulus 
operates.     That  is,  for  sight  and  hearing  he  refers  it  to  space;  for  the 
nerves  of  taste,  smell,  or  touch,  he  refers  it  to  the  peripheral  regions 
of  his  body,  even  if  these  be  lacking.     Thus,  in  an  amputated  leg,  pain 
in  the  stump  is  referred  to  the  toes.     This  is  the  law  of  eccentric 
projection  of  sensation. 

Touch. 

The  organ  of  touch  is  represented  by  the  skin  and  mucous  mem- 
branes in  proximity  to  the  natural  orifices  of  the  body. 


480  PHYSIOLOGY. 

The  skin,  or  common  integument,  is  composed  of  the  following 
layers:  (1)  the  epidermis;  (2)  the  corium ,  or  cutis  vera,  with  its 
papillae;  and  (3)  the  subcutaneous  tissue  with  the  adipose  tissue. 

1.  The  Epidermis  belongs  to  the  tissues  which  are  composed  of 
simple  cells  united  to  each  other  by  cement-substance.     It  in  itself 
consists  of  several  layers : — 

(a)  Stratum  corneum.     This  is  the  superficial  horny  layer  and 
consists  of  several  layers  of  horny  scales,  without  any  nucleus.    The 
layers  are  separated  from  one  another  by  narrow  clefts  containing  air. 
They  are  in  a  process  of  desquamation.     The  variable  thickness  of 
the  epidermis  is  chiefly  dependent  upon  the  thickness  of  this  outer 
layer.     The  stratum  corneum  is  of  greater  thickness  on  the  palm  of 
the  hand  and  fingers,  and  sole  of  the  foot. 

(b)  The  stratum  tucidum  is  clear  and  transparent  and  consists 
of  a  few  layers  of  clear  cells  which  contain  but  the  remains  of  nuclei. 

(c)  Stratum  Granulosum. — Under  this  is  the    (d)   rete  muco- 
sum,  or  rete  Malpighii.     This  layer  consists  of  strata  of  nucleated, 
protoplasmic,  epithelial  cells.     In  the  colored  races  these  contain 
pigment.     Among  the  fair  races  this  layer  of  the  skin  of  the  scrotum 
and  anus  contains  pigment-granules.     The  deeper  cells  are  more  or 
less  polyhedral,  while  the  deepest  ones  are  columnar.     These  last  are 
placed  vertically  upon  the  papillae  and  are  provided  with  spherical 
nuclei.     Granular  leucocytes  or  wandering  cells  are  occasionally  found 
between  these  cells. 

The  superficial  layers  of  the  epidermis  are  continually  being 
thrown  off,  while  new  cells  are  just  as  rapidly  being  formed  in  the 
deep  layers.  Within  them  there  occurs  a  proliferation  of  the  cells  of 
the  rete  Malpighii.  Many  of  the  cells  exhibit  the  changes  of  karyo- 
kinesis.  No  pigment  is  formed  within  the  epidermis  itself.  But  in 
brunettes  and  colored  races  pigment  granules  of  melanin  exist  within 
the  cells  of  the  lowermost  layers  of  the  stratum  Malpighii.  The 
pigment-granules  present  here  have  been  carried  thither  by  leucocytes 
from  the  subcutaneous  tissue.  This  explains  how  a  piece  of  white 
skin  transplanted  to  a  colored  person  becomes  black. 

2.  The  Corium,  or  cutis  vera,  is  a  dense  network  of  fibrous  con- 
nective tissue  admixed  with  elastic  fibers.    Its  entire  surface  is  studded 
with  numerous  papillae,  the  largest  of  which  are  upon  the  volar  surface 
of  the  hand  and  foot.    The  majority  of  the  papillae  contain  a  looped 
capillary.     In  some  regions  of  the  surface  of  the  body  they  contain 
touch-corpuscles.    The  papillae  are  arranged  in  groups  whose  disposi- 
tion varies  in  the  several  parts  of  the  body. 


TACTILE  SENSE.  481 

The  lowermost  connective-tissue  layers  of  the  corium  gradually 
merge  into  the  subcutaneous  tissue.  Its  arrangement  is  such  as  to 
leave  spaces  which  contain,  for  the  most  part,  cells  of  fat.  The  sub- 
cutaneous connective  tissue  composed  of  ordinary  connective  tissue, 
is  soft,  and  is  rich  in  adipose  cells,  vessels,  nerves,  and  lymphatics. 

Tactile  Corpuscles. — The  student  well  knows  that  in  the  epithe- 
lium of  the  skin  and  mucous  membranes  the  nerves  of  common  sen- 
sation are  arranged,  for  the  most  part,  in  networks  of  fibrillse.  In 
addition  to  these  there  are  other  special  terminal  organs  of  sensory 
nerves.  These  are  variously  known  as  tactile  corpuscles.  These  are 
concerned  in  the  perception  of  some  special  quality  or  quantity  of 
sensory  impulses.  They  have  their  site,  not  in  the  surface  of  the 
epidermis,  but  deeper  within  the  tissues.  The  principal  ones  among 
thorn  are  the  corpuscles  of  Pacini,  the  end-bulbs  of  Kmuse,  and  the 
corpuscles  of  Meissner. 

The  tactile  corpuscles  of  Meissner  in  the  papilla  of  the  cutis 
vera  are  oval  bodies  1/30  inch  in  length  and  nearly  the  same  width. 
These  are  the  corpuscles  of  the  palm  of  the  hand  and  sole  of  the 
foot.  One  or  two  medullated  nerve-fibers  are  spirally  twisted  around 
it,  and  near  the  top  of  the  corpuscles  the  nerves  lose  their  white 
substance  and  the  axis-cylinders  end  in  flat  bodies  penetrating  the 
surface  of  the  corpuscle.  The  corpuscle  is  composed  of  flattened 
cells,  which  give  it  a  striated  appearance.  These  corpuscles  are  built 
up  of  a  great  number  of  tactile  discs  and  of  tactile  cells.  There  are 
about  twenty  tactile  corpuscles  to  a  square  millimeter  of  the  skin. 

The  Pacinian  or  Yater's  corpuscles  are  attached  in  greatest  num- 
ber along  the  digital  nerves  of  the  fingers  and  toes  and  occasionally  on 
other  nerves.  These  bodies  are  oval  or  pyriform,  about  1/8  inch  in 
length  and  1/12  inch  in  thickness.  They  have  a  pearly  luster  and 
consist  of  a  series  of  capsules  or  concentric  layers  of  fibrous  tissue, 
with  here  and  there  a  nucleus.  The  outer  capsules  are  separated 
more  widely  than  the  inner  ones  and  the  interspaces  are  filled  with 
a  colorless  liquid.  Each  corpuscle  is  attached  to  a  nerve  by  a  pedicle 
of  fibrous  tissue  through  which  exetends  a  single  nerve-fiber,  which, 
penetrating  the  series  of  capsules,  terminates  by  sending  its  neuraxon 
into  the  central  cavity  of  the  corpuscle,  at  the  top  of  which  it  ends  in 
a  simple  extremity.  Each  corpuscle  is  covered  with  forty  or  fifty 
capsular  layers. 

Krause's  End-bulbs. — The  tactile  corpuscles  of  Krause  are  elon- 
gated, oval  bodies,  into  one  end  of  which  a  nerve-fiber  penetrates. 
Externally  they  have  a  covering  of  connective  tissue,  a  continuation 


482  PHYSIOLOGY. 

of  the  perineurium,  and  an  internal  knob  of  granular  matter  dis- 
posed in  concentric  layers  with  a  few  nuclei.  In  the  center  of  this 
knob  is  found  the  axis-cylinder  which  runs  through  it  like  a  ribbon 
to  the  upper  pole  and  then  ends  in  a  slight  thickening.  These  bulbs 
are  found  in  the  basement  membrane  of  certain  mucous  membranes, 
as  in  the  corneal  conjunctiva,  in  the  mucous  membrane  of  the  mouth, 
in  the  clitoris,  and  in  the  glans  penis.  They  are  also  to  be  found  in 
the  skin. 

Corpuscles  of  Grandry  or  Merkel  consist  of  two  or  more  flattened 
cells,  each  larger  than  a  simple  tactile  cell.  Each  cell  is  nucleated, 
and  the  nerve-fiber,  before  entering  the  corpuscle,  loses  its  white 
sheath,  and  the  axis-cylinder  ends  as  a  flat  disc  lying  between  the 
two  tactile  cells.  These  tactile  cells  are  piled  one  upon  the  other  so 
as  to  form  a  heap  of  cells.  They  are  found  chiefly  in  the  beak  and 
tongue  of  the  duck  and  in  the  epiderm  of  man. 

Other  Modes  of  Ending. — In  addition  to  sensory  nerves  ending 
by  special  structures  as  those  just  described,  there  are  some  which  do 
not  possess  such  elaborate  apparatus.  In  the  case  of  many  nerves, 
the  axis-cylinder  splits  up  into  fibrils  which  are  arranged  in  the  form 
of  a  network.  From  this  somewhat  deeply  placed  network  very  fine 
fibrils  or  fibrillae  are  given  off  to  terminate  in  the  tissues  to  be  sup- 
plied. The  fibrillae  have  their  terminus  in  free  ends  lying  between 
the  epithelial  cells.  In  many  cases  the  free  ends  are  seen  to  be  pro- 
vided with  small  enlargements.  These  latter  are  known  as  tactile 
cells. 

Knowledge  Gained. — By  the  sense  of  touch  one  feels  the  contact 
of  bodies  and  their  temperature,  whether  these  bodies  be  solid,  liquid, 
or  gaseous.  This  special  sense  also  defines  at  the  same  time  the 
locality  of  the  impression  made  by  the  external  agent.  The  judgment 
of  locality  is  not,  however,  free  from  error.  It  is  really  exact  for 
but  a  few  points;  that  is,  wherever  the  touch  is  delicate.  On  the 
other  parts  of  the  skin  the  individual  never  exactly  divines  the  point 
pressed  upon;  so  that  he  makes  mistakes  of  millimeters,  centimeters, 
and  even  decimeters. 

In  sensory  nerve-trunks  there  exist  different  kinds  of  nerve-fibers ; 
some  administer  to  painful  impressions  and  others  to  tactile  impres- 
sions. Sensations  of  temperature  and  muscular  sense  belong  to  the 
latter  group. 

SENSE  SPOTS. — The  surface  of  the  skin  is  found  by  experimenta- 
tion to  be  composed  of  very  small  sensorial  areas.  Between  these  areas 
are  found  little  fields  which  are  insensitive  and  which  are  relatively 


TACTILE  SENSE.  483 

much  larger  than  the  sensitive  areas,  or  "spots."  It  has  been  dem- 
onstrated that  each  "spot"  has  its  own  specific  function  to  perform, 
whether  that  be  touch,  cold,  warmth,  or  pain.  Each  little  sensitive 
area  no  doubt  marks  the  site  of  single  or  groups  of  sensory  corpuscles, 
end-organs,  or  bulbs,  of  the  terminations  of  various  nerves.  Where 
the  nerves  terminate,  there  are  the  sense-spots  represented  upon  the 
skin's  surface. 

Some  one  has  very  aptly  likened  the  skin  with  its  sense-spots  to 
a  pond  upon  whose  surface,  as  well  as  just  below  the  same,  are  seen 
lily  leaves  floating.  The  leaves  represent  the  sense-spots.  A  pebble 
thrown  into  the  pond  may  strike  one  or  more  leaves,  depending  upon 
how  close  together  they  are  growing.  The  pebble  represents  a  stim- 
ulus, and  by  its  presence  temporarily  stirs  up  or  throws  into  a  state 
of  excitation  the  leaves  struck  as  well  as  some  of  those  adjacent. 

Upon  the  skin's  surface  may  be  demonstrated  "touch-spots," 
"cold-spots,"  "warmth-spots,"  and  "pain-spots."  These  are  all 
mixed  up,  though  those  of  one  kind  may  be  more  strongly  in  evi- 
dence in  certain  areas.  As  a  rule,  "pain-spots"  are  found  to  be  the 
most  numerous ;  "  warmth-spots  "  are  the  least  likely  to  be  found. 

SOLIDS. — These  act  upon  the  sense  of  touch  either  by  pressure  or 
by  traction.  Pressure  may  be  from  zero  to  a  maximum  whose  limit  is 
the  disorganization  of  the  tissues.  Up  to  a  certain  minimum,  which 
depends  upon  the  sensibility  of  the  region,  the  application  of  pressure 
excites  no  sensation.  The  minimum  pressure  corresponds  to  the 
sensation  of  simple  contact;  this  by  degree's  gives  way  to  the  sensa- 
tion of  pressure.  When  the  pressure  is  sufficiently  increased  there 
results  pain.  This  in  turn  disappears  when  the  pressure  is  increased 
to  disorganization  of  the  tissues. 

Pressure  varies  not  only  in  intensity,  but  in  extent.  No  matter 
how  the  latter  may  be  limited,  the  pressure  always  affects  at  least 
more  than  one  peripheral  nerve-ending. 

When  tactile  sensations  are  very  light  and  succeed  one  another 
rapidly,  a  large  number  of  nerves  is  stimulated.  The  sensation  ex- 
cited is  a  peculiar  one :  that  of  tickling. 

Traction  upon  the  hair  and  nails  determines  pain  much  more 
rapidly  than  does  pressure. 

LIQUIDS. — Liquids  applied  at  the  temperature  of  the  skin  exercise 
a  uniform  pressure  upon  all  parts  of  the  cutaneous  surface  excepting 
those  at  the  level  of  the  surface  of  the  fluid. 

If  a  finger  be  plunged  into  a  heavy  fluid,  as  metallic  mercury,  the 
part  submerged  bears  a  pressure  which  decreases  from  below  upward 


484  PHYSIOLOGY. 

uniformly.  It  is  only  at  the  surface  of  the  liquid  that  a  marked 
inequality  of  pressure  exists.  It  follows  a  circular  line  which  sur- 
rounds the  finger  at  this  level  and  can  be  plainly  felt  by  the  indi- 
vidual. If  a  lighter  fluid,  as  water,  be  used,  the  pressure  sensation 
is  but  very  slight. 

COMPOUND  TACTILE  SENSATIONS. — These  may  be  simultaneous 
or  successive.  Simultaneous  tactile  sensation  may  be  either  double 
or  multiple.  Double  sensations,  whether  of  contact,  pressure,  or 
traction,  are  shown  only  when  the  stimuli  are  applied  at  a  certain 
distance  from  one  another.  If  the  stimuli  be  near  enough,  the  sensa- 
tion remains  single  even  though  the  stimulus  has  been  applied  to  the 
skin  in  two  places.  The  earliest  systematic  experiments  upon  this 
subject  were  by  Weber.  He  touched  the  various  points  of  the  skin's 
surface  with  a  pair  of  carpenter's  compasses  and  then  observed  the 
distance  of  separation  necessary  to  give  a  distinct  impression  of  two 
points  of  contact.  The  instrument  now  used  for  this  purpose  is  the 
cesfhesiometer.  From  the  table  compiled  by  Weber  it  is  found  that 
the  tip  of  the  tongue  is  most  sensitive,  while  the  thigh  and  arm  are 
least  so.  In  the  case  of  the  tongue,  the  minimum  separation  neces- 
sary for  the  impression  of  double  contact  is  but  1.1  millimeters;  67.6 
millimeters  are  necessary  in  the  case  of  the  thigh  and  arm.  The 
connection  between  the  mental  and  physical  conditions  explains  cer- 
tain illusions  of  tactile  sensations.  Of  these,  the  best  known  is  the 
so-called  experiment  of  Aristotle.  When  a  pea  or  small  ball  is  rolled 
between  the  crossed  index*  and  middle  fingers  of  a  blindfolded  person 
there  results  a  sensation  of  two  balls  being  present  instead  of  one. 

There  are  spots  of  temperature  which  have  been  worked  out  by 
Goldscheider.  They  are  found  to  be  arranged  in  a  linear  manner 
and  generally  radiate  from  certain  points  of  the  skin,  usually  the 
hair-roots.  The  chain  of  "  cold-spots  "  does  not  coincide  with  those 
of  "warmth-spots."  The  sensation  of  cold  occurs  at  once;  that  of 
heat  develops  gradually.  As  a  rule,  the  cold-spots  are  more  abund- 
ant over  the  entire  body  surface.  The  hot-spots  may  be  quite  absent. 
The  minimal  distance  on  the  forehead  for  cold-spots  is  0.8  milli- 
meter, while  for  warmth-spots  it  is  5  millimeters. 

Protection  of  the  Organs  of  Touch. 

The  means  are  the  cutaneous  oil  and  the  horny  appendages.  The 
cutaneous  oil  is  the  product  of  the  sebaceous  glands  of  the  skin. 
They  are  found  in  every  area  of  the  skin,  but  are  less  numerous  than 
the  sudorific  glands  except  in  the  palms  of  the  hands  and  soles  of  the 


TACTILE  SENSE.  485 

feet.  They  may  be  large,  as  in  the  nose;  these  usually  have  fine, 
downy  hairs  near  their  mouths. 

The  sebaceous  glands  are  situated  more  superficially  than  the 
sweat-glands.  They  are  white  granules  annexed  to  the  hair-follicle, 
in  which  their  excretory  duct  ends.  Their  size  is,  in  general,  in- 
verse to  the  volume  of  the  corresponding  hair-follicle.  Where  the 
hairs  are  large  the  sebaceous  glands  seem  to  be  appendages,  and  when 
the  hairs  are  small  its  hair-follicle  seems  to  be  an  appendage  of  the 
sebaceous  gland.  The  glands  are  aciniform,  surrounded  by  a  thin, 
connective  tissue  with  a  basement  membrane  studded  with  epithelial 
cells  infiltrated  with  fat,  and  the  cells  are  more  fatty  in  the  direction 
of  the  excreting  duct,  where  is  found  free  fat,  due  to  the  destruction 
of  the  cells.  When  the  sebaceous  secretion  stagnates,  it  forms  a  fat- 
like  mass  which,  when  expressed,  as  in  the  nose,  forms  the  comedo,  a 
wormlike  body.  The  black-heads,  as  they  are  called,  consist  of  dirt 
in  the  surface  of  the  gland.  When  the  comedo  is  expressed  the  duct 
has  been  mistaken  as  the  head  of  the  worm.  The  sebaceous  matter 
contains,  even  in  healthy  individuals,  the  pimple-mite,  or  Demodex 
folliculorum. 

There  are  three  varieties  of  sebaceous  secretions :  (1)  that  of  the 
skin,  (2)  the  vernix  caseosa  of  the  newborn  child,  and  (3)  the  smegma 
of  Tyson's  glands  of  the  prepuce. 

Function. — The  sebaceous  matter  anoints  the  hairs  with  oil  in 
their  progress  of  growth  from  the  skin.  The  greasiness  of  the 
surface  of  the  skin  caused  by  this  secretion  permits  the  dust  readily 
to  adhere,  which  makes  soap  necessary  to  remove  its  excess.  Seba- 
ceous secretion  is  made  up  of  olein,  palmitin,  cholesterin,  and  earthy 
phosphates. 

The  organ  of  touch  is  also  protected  by  the  horny  layer  of  the 
epidermis,  whose  cells  are  being  constantly  removed  by  friction  and 
as  constantly  renewed  by  proliferation  of  the  cells  of  the  cutis  vera. 

The  modifications  of  the  epidermis  in  man  are  the  hair  and  nails. 

Hair. — The  hairs  are  threadlike  appendages  to  the  skin  project- 
ing from  almost  every  part  of  its  surface  except  the  palms  and  soles. 
They  are  flexible,  elastic,  and  shining,  but  vary  in  degree  of  develop- 
ment, .fineness,  color,  and  form  in  different  races  and  the  sexes  as 
well  as  in  different  persons.  The  color  of  the  hair  varies  from  a  light 
color  to  a  black.  The  black  hairs  are  found  in  all  parts  of  the  globe 
and  in  all  latitudes,  as  in  the  Esquimaux,  negro,  Indian,  and  Malay. 
All  the  colored  races  have  black  hair,  and  this  is  true  in  some  groups 
of  the  white  race.  Bed  hair  is  represented  in  all  races.  The  hair  is 


486  PHYSIOLOGY. 

composed  of  a  projecting  part,  the  stem,  terminated  by  the  point,  or 
end.  The  portion  inserted  into  the  skin  is  the  root,  which  begins  in  a 
clublike  expansion.  The  hairs  generally  project  obliquely  from  the 
skin.  The  hairs  of  the  white  race  are  cylindrical;  the  hair  of  the 
negro  flattened  cylindrical.  In  structure  the  hairs  consist  of  an  ex- 
terior cuticle,  a  cortex,  and  an  interior  medulla.  The  cuticle  consists 
of  a  single  layer  of  thin,  colorless,  quadrilateral  scales  which  overlap 
like  the  shingles  of  a  roof.  The  edges  of  the  scales  are  directed  up- 
ward and  outward  along  the  shaft.  The  cortex  makes  the  chief  part 
of  the  hair,  and  it  is  that  upon  which  the  color  of  the  hair  mainly 
depends  in  different  individuals.  The  cortical  layer  is  made  oip  of 
elongated,  fusiform  cells  containing  a  lineal  nucleus.  When  the  color- 
ing matter  disappears  in  the  cortex  the  hair  becomes  white.  The 
medulla  is  frequently  absent,  especially  in  the  dark-colored  hairs.  It 
occupies  the  axis  of  the  hair.  It  consists  of  cuboidal  cells  with  gran- 
ular contents  and  an  indistinct  nucleus.  The  medullary  substance  is 
generally  mingled  with  more  or  less  air,  in  small  bubbles,  which  pene- 
trates from  the  ends  of  the  hairs  and  gives  to  these  when  white  the 
characteristic  silver  luster.  The  root  of  the  hair  is  lodged  in  a  flask- 
shaped  receptacle  of  the  skin  called  the  hair-follicle,  at  the  bottom  of 
which  is  a  papilla  from  which  the  hair  grows.  "  Goose-flesh  "  is  due 
to  minute  muscles  contracting  and  causing  the  hair-follicles  to  become 
erect.  At  the  same  time  the  sebaceous  glands  are  compressed,  favor- 
ing the  exudation  of  the  sebaceous  secretion. 

Chemically,  the  hairs  are  mainly  composed  of  an  albuminoid  de- 
rivative, keratin,  in  which  a  notable  quantity  of  sulphur  is  present : 
about  5  per  cent.  In  the  ashes  are  found  the  phosphates,  earthy 
sulphates,  oxide  of  iron,  and  pigment. 

FUNCTION. — The  large  hairs  serve  to  protect  the  skin,  breaking 
shocks  and  preventing  a  considerable  loss  of  heat.  In  other  places, 
like  the  armpits,  they  prevent  friction  and  attrition  of  the  skin  layers. 
The  downlike  hairs  render  the  touch  more  delicate. 

Nails. — The  nails  are  hard  appendages  of  the  skin,  and  corre- 
spond to  the  claws  of  other  animals.  They  are  flexible,  translucent, 
square-shaped  plates  continuous  with  the  epiderm  and  resting  on  a 
depressed  surface  of  the  dermis  called  the  matrix,  or  bed. 

The  exposed  part  of  the  nail  is  the  Body  and  its  anterior  end  is 
its  free  border.  The  root  of  the  nail  is  lodged  in  a  deep  groove  of 
the  matrix  and  the  lateral  borders  are  received  into  shallow  grooves. 
The  half -moon,  or  lunule,  of  the  nail  is  due  to  a  less  degree  of  vascu- 
larity  of  the  matrix  at  the  root  defined  by  a  semicircular  line.  The 


TACTILE  SENSE.  487 

horny  layer  corresponds  to  the  cuticle  of  the  epiderm,  and  is  com- 
posed of  flattened,  nucleated  cells.  The  soft  layer  of  the  nails,  the 
stratum  mucosum,  corresponds  to  that  layer  of  the  epiderm.  The 
nails  grow  in  length  by  new  cells  at  the  root,  in  thickness  by  additions 
beneath  the  nail. 

The  nails  serve  to  protect  the  skin  at  the  tips  of  the  phalanges, 
and,  at  the  same  time,  perfect  the  touch  of  the  fleshy  parts  of  the 
flngers.  The  average  growth  of  the  nails  is  about  one-eighth  of  an 
inch  per  month. 


CHAPTER  XVI. 

SPECIAL  SENSES  (Continued). 
THE  SENSE  OF  TASTE. 

TASTE  is  an  organ  of  special  sense,  by  which  as  a  medium  the 
individual  perceives  savory  impressions.  Its  principal  uses  to  the 
economy  are  two:  First,  it  acts  as  a  guide  to  the  individual  in  his 
choice  of  food,  at  the  same  time,  rendering  its  mastication  a  matter 
of  some  pleasure.  Secondly,  it  excites  the  salivary  glands  reftexly,  so 
that  they  pour  out  their  juices  into  the  mouth. 

The  organ  of  taste  is  seated  in  the  oral  cavity  and  in  the  mucous 
membrane  of  the  tongue.  Its  limits  are  not  well  denned.  The  diffi- 
culty in  their  determination  depends  upon  the  double  fact  that  these 
organs  of  taste  are  endowed  with  a  very  delicate  sensibility  of  a 
tactile  nature,  and  that  the  gustatory  sensibility  and  the  organ  of 
smell  are  in  very  close  proximity  to  one  another.  For  these  reasons 
one  may  very  easily  believe  that  certain  regions  of  his  mouth  are 
gustatory,  when  in  reality  the  substances  which  have  touched  them 
have  only  produced  tactile  or  olfactory  impressions. 

Still  it  has  been  shown  that  the  principal  regions  of  the  oral 
mucous  membrane  designed  to  perceive  taste-impressions  are  at  the 
base  and  edges  of  the  tongue.  In  a  secondary  degree,  also,  gustatory 
impressions  are  perceived  in  the  anterior  surface  and  edge  of  the  soft 
palate,  and  the  anterior  portion  of  the  tongue.  All  other  portions 
of  the  mouth  are  incapable  of  taste-impressions. 

The  Tongue. — The  principal  organ  of  the  sense  of  taste  is  un- 
doubtedly the  tongue.  Its  anatomical  structure  as  a  muscular  organ 
has  already  been  described  when  discussing  deglutition  and  the  part 
it  played  in  the  role  of  that  important  function.  At  this  time  it 
remains  but  to  review  such  portions  as  have  a  direct  bearing  upon 
its  role  as  a  gustatory  member. 

There  are  three  kinds  of  papillae  in  the  mucous  membrane  of  the 
tongue :  the  circumvallate.,  fungiform,  and  filiform.  They  extend  from 
the  tip  of  the  tongue  to  the  foramen  ca3cum.  The  papillae  consist 
of  elevations,  visible  to  the  naked  eye  and  covered  with  stratified, 
squamous  epithelium.  The  central  body  of  each  papilla  contains 
connective  tissue,  blood-  and  lymph-  vessels,  and  nerves. 
(488) 


THE  SENSE  OF  TASTE.  489 

The  circumvallate  papillse,  the  largest  of  the  varieties  and  about 
a  dozen  in  number,  form  a  V-like  row,  defining  the  papillary  layer  at 
the  posterior  third  of  the  tongue.  They  have  the  form  of  an  inverted 
cone  surrounded  by  a  ringlike  wall-elevation. 

The  fungiform  are  next  in  size,  and  more  numerous  than  the 
circumvallate.  They  are  small,  red  eminences  scattered  over  the  sur- 
face of  the  tongue,  but  are  especially  numerous  at  and  near  the  tip. 
They  are  rounded  at  the  free  extremity  and  narrower  at  the  point  of 
attachment  to  the  tongue. 

The  filiform  papillae,  smaller  and  more  numerous  than  the  others, 
are  crowded  in  the  spaces  between  the  others,  but  are  arranged  in 
rows  diverging  from  the  median  line  of  the  tongue. 

Nerves.  —  The  tongue  receives  three  nerves :  one  of  motion,  the 
liypoglossal,  which  animates  the  muscles;  and  two  other  sensory 
branches — the  lingual  branch  of  the  glosso-pharyngeal  and  the  lingual 
branch  of  the  trigeminus.  The  former  of  the  latter  two  branches 
spreads  in  the  mucous  membrane  at  the  base  and  edges  of  the  tongue ; 
the  latter  is  distributed  to  the  mucous  membrane  of  the  anterior  two- 
thirds  of  the  tongue.  The  branches  of  the  glosso-pharyngeal  are  espe- 
cially concerned  in  sensations  of  bitterness,,  while  the  branches  of  the 
trigeminus  are  affected  principally  by  sweet  and  acid  tastes. 

Section  of  the  hypoglossal  upon  both  sides  causes  .paralysis  of  the 
tongue  without  injuring  its  tactile  or  gustatory  sensibilities.  Section 
of  the  lingual  branch  of  the  trigeminus  causes  only  loss  of  fine  tactile 
sensibility  and  gustatory  sensibility  of  the  anterior  two-thirds  of  the 
tongue. 

Section  of  the  glosso-pharyngeal  causes  loss  of  tactile  and  gusta- 
tory sensibility  in  the  mucous  membrane  at  the  base  of  the  tongue. 
Such  an  animal  can  swallow  bitter  and  nauseous  substances,  like 
colocynth,  with  impunity. 

The  gustatory  action  of  the  lingual  branch  of  the  trigeminus 
comes  from  the  chorda  tympani.  The  latter  is  a  small  nerve  which' 
begins  in  the  facial  and  traverses  the  middle  ear  to  join  the  lingual 
branch  at  the  level  of  the  pterygoid  muscles. 

The  chorda  tympani  nerve  passes  from  the  tongue  to  the  nerve- 
centers  through  the  lingual  nerve,  the  facial,  and  finally  through  the 
intermediate  nerve  of  Wrisberg. 

Taste-organs. — The  terminal  branches  of  the  glosso-pharyngeal 
nerve  end  in  the  taste-bulbs.  The  taste-bulbs  are  oval  bodies  imbedded 
in  the  epithelial  layer.  Each  taste-bulb  is  formed  of  two  kinds  of 
elongated  epithelial  cells,  and  their  whole  outline  is  barrel-shaped. 


490 


PHYSIOLOGY. 


The  taste-cells  are  narrow  and  slightly  thickened  in  the  middle,  where 
the  nucleus  is  situated.  The  taste-bulbs  occur  chiefly  on  the  sides  of 
the  circumvallate  papilla,  although  a  small  number  of  them  are  on 
the  fungiform  and  the  soft  palate.  Tlie  end  of  the  taste-bulbs  near  the 
surface  have  a  minute,  funnel-like  opening  called  the  taste-pore.  The 
number  of  taste-bodies  is  very  great.  If  the  glosso-pharyngeal  nerve 
is  cut,  the  taste-bodies  degenerate. 

The  proper  stimuli  for  the  end-bulbs  of  the  gustatory  nerves  are 
the  savory  substances.  These  must  be  dissolved  in  the  liquids  of  the 
mouth  before  they  can  penetrate  the  outer  cells  of  the  mucous  mem- 
brane to  come  into  contact  with  the  nerve-filaments  in  the  imbedded 


Fig.  115. — Structure  of  the  Taste-organs.     (LANDOIS.) 

I.  Transverse  section  of  a  circumvallate  papilla.  W,  the  papilla,  v,  v,  The 
wall  in  sections.  R,  R,  The  circular  slit,  or  fossa.  K,  K,  The  taste-bulbs  in 
position.  N,  N,  The  nerves. 

•  II.  Isolated  taste-bulbs.     D,   Supporting,   or  protective,    cells.     K,   Lower 
end.    E,  Free  end,  open,  with  the  projecting  apices  of  the  taste-cells. 

III.  Isolated  protective  cell  (d)  with  a  taste-cell  (e). 

bulbs.  The  most  suitable  temperature  for  the  thorough  testing  of 
liquids  is  100°  F. 

The  intensity  of  the  gustatory  impression  depends  upon  various 
factors :  the  nature  of  the  substance,  the  duration  of  the  impression, 
sensibility  of  the  region  touched,  and  the  stimulating  action  of  the 
substance  upon  the  mucous  membrane.  The  flavor  of  a  substance 
does  not  depend  upon  its  chemical  properties,  for  both  quinine  and 
sulphate  of  magnesia  are  bitter;  sugar,  chloroform,  and  glycerin  are 
sweet. 

Improper  stimuli  give  gustatory  impressions.  Thus,  the  galvanic 
current  applied  to  the  tongue  gives  an  acid  taste  at  the  positive  pole 
and  a  weaker,  alkaline  taste  at  the  negative  pole. 


THE  SENSE  OF  TASTE.  491 

Varieties  of  Substances. — Of  the  gustatory  substances  there  are 
four:  (1)  sweet,  (2)  Utter,  (3)  acid,  and  (4)  saline.  In  addition 
to  these  fundamental  substances  there  are  compound  gustatory  im- 
pressions, or  a  confusion  of  gustatory  sensations  with  those  which  are 
tactile  or  olfactory.  Thus,  there  is  known  the  piquant  taste  of  cheese, 
the  caustic  taste  of  mustard,  and  the  aromatic  taste  of  strawberries. 

The  acid  and  sweet  tastes  are  best  perceived  at  the  tip  and  edges 
of  the  tongue;  the  salty  and  bitter  tastes  are  comprehended  at  the 
base.  This  leads  to  the  result  that  some  substances  have  a  different 
taste,  dependent  upon  whether  they  touch  the  tip  or  the  base  of  the 
tongue.  Thus,  acetate  of  potassium  at  the  tip  of  the  tongue  is  acid, 
and  at  the  base  it  is  bitter. 

The  four  primitive  tastes  are  not  all  perceived  at  the  exact  time 
of  their  impression  upon  the  tongue.  The  salty  is  first  perceived, 
then  the  sweet,  next  the  acid,  and  last  the  bitter. 

Tactile  sensations  by  astringents  (tannic  acid)  or  thermal  sensa- 
tions (mustard)  are  usually  confounded  with  taste  proper.  The  taste 
of  vanilla  is  but  an  olfactory  impression. 

Drugs. — By  the  action  of  drugs  one  is  able  to  abolish  certain 
tastes  more  readily  than  others.  Cocaine  upon  the  tongue  abolishes 
tactile  sensations  and  the  taste  for  bitter  things,  but  does  not  interfere 
with  voluntary  movement. 

The  leaves  of  Gymnema  sylvestre,  when  chewed,  destroy  the  sense 
of  taste  for  bitters  and  sweets,  while  that  for  salts  and  acids  remains. 

The  Taste-center,  to  which  the  gustatory  nerves  send  their  im- 
pressions, lies  in  the  uncinate  gyrus. 


CHAPTER  XVII. 

SPECIAL   SENSES    (Continued). 

THE  SENSE  OF  SMELL. 

THE  seat  of  the  sense  of  smell  resides  in  the  cavities  of  the  nose. 
Kant  has  very  aptly  spoken  of  smell  as  "taste  at  a  distance." 

The  organ  of  smell  resembles  those  of  sight  and  hearing  in  that 
it  consists  of  a  special  nerve  which  ends  in  a  specialized  epithelium. 
In  this  case  the  special  nerve  is  the  olfactory;  the  specialized  epithe- 
lium is  the  mucous  membrane  of  the  upper  portion  of  the  nasal 
cavity.  It  is  in  this  portion  of  the  mucous  membrane  that  the  fila- 
ments of  the  olfactory  nerve  are  distributed.  For  that  reason  it  has 
been  termed  the  regio  olfactoria,  and  comprises  the  upper  portion  of 
the  septum,  the  upper  turbinated,  and  part  of  the  middle  turbinated 
regions.  All  other  portions  of  the  nasal-cavity  covering  is  known  as 
the  regio  respiratoria,  or  simply  the  Schneiderian  membrane.  During 
ordinary  respiration  the  currents  of  air  in  their  passage  in  and  out 
are,,  for  the  most  part,,  confined  to  this  latter  region.  The  mucous 
membrane  which  covers  this  portion  of  the  nasal  cavity  is,  in  struc- 
ture and  appearance,  very  similar  to  that  of  the  trachea.  It  is  com- 
posed of  layers  of  ciliated  epithelium  which  rest  upon  a  basement 
membrane  rich  in  blood-vessels  and  tymphatics.  Among  the  ciliated 
cells  are  found  numerous  goblet  and  mucous  cells  whose  secretions 
keep  the  surface  of  the  mucous  membrane  soft  and  moist.  In  it  are 
numerous  filaments  of  the  trigeminus  which  endow  it  with  tactile 
sensibility.  There  are  no  filaments  of  the  olfactory  nerve  in  this 
region. 

The  olfactory  mucous  membrane  is  thicker  than  that  of  the 
respiratory  portion.  To  the  naked  eye  it  presents  a  yellow  or  brown- 
yellow  color  because  of  the  pigment  contained  within  it.  By  reason 
of  its  color  it  is  very  readily  distinguished  from  that  of  the  Schneide- 
rian membrane.  Its  surface  is  covered  by  a  single  layer  of  cylindrical 
epithelium  whose  cells  are  often  branched  at  their  lower  ends. 

The  olfactory  region  contains  the  olfactory  cells.     These  possess 
a  body  of  spindle  shape  with  a  large  nucleus  containing  nucleoli.     In 
the  deeper  part  the  olfactory  cells  pass  into  and  become  continuous 
with  fine  fibers.     These  last  pass  into  the  olfactory  nerve. 
(492) 


THE  SENSE  OF  SMELL.  493 

The  olfactory,  the  nerve  of  smell,  issues  by  two  roots,  each  from 
the  corresponding  hemisphere.  The  fibers  are  composed  of  medullated 
and  nonmedullated  fibers. 

These  latter  fibers  proceed  from  the  olfactory  bulb. 

The  olfactory  bulb  is  a  part  of  the  cerebral  cortex  and  is  an  oval 
or  club-shaped  mass  of  gray  matter  which  rests  on  the  cribriform 
plate  of  the  ethmoid  bone,  through  the  foramen  of  which  it  is  con- 
nected with  the  olfactory  nerves.  The  olfactory  nerves  are  twenty 
in  number  and  are  the  central  coursing  of  the  neuraxons  of  the  rod- 
shaped  olfactory  nerve-cells  in  the  olfactory  region  of  the  nose.  They 
pass  through  the  openings  in  the  cribriform  plate  and  terminate  in 
arborizations  about  the  dendrons  of  the  mitral  cells  of  the  olfactory 
glomeruli.  These  bipolar  cells  greatly  resemble  the  cells  of  a  ganglion 
of  a  posterior  root  of  the  spinal  cord,  one  neuraxon  going  to  the 
olfactory  mucous  membrane  and  the  central  neuraxon  connecting  with 
the  olfactory  bulb. 

The  olfactory  bulb  from  without  inward  consists  of  four  layers : — 

1.  The  nerve-fibers. 

2.  Stratum  glomerulosum. 

3.  Stratum  gelatinosum. 

4.  Layer  of  central  nerve-fibers. 

In  the  first  layer  each  fibril  is  a  central  neuraxon  of  a  rod-shaped 
nerve-cell  from  the  olfactory  mucous  membrane.  .  The  fibers  of  the 
olfactory  nerves  pass  into  the  glomeruli  lying  beneath.  Within  the 
glomerulus  the  endings  of  the  olfactory  fibril  come  in  contact  with  an 
olfactory  end-brush  of  an  apical  dendron  of  a  mitral  cell. 

In  the  stratum  glomerulosum  each  glomerulus  consists  of  the 
terminal  arborizations  of  an  olfactory  nerve-fiber,  together  with  the 
olfactory  end-brushes  from  the  apical  dendrons  of  the  mitral  cells. 

The  stratum  gelatinosum  in  its  inner  part  contains  two  chief 
forms  of  cells:  the  deep  and  superficial  layers  of  mitral  cells  which 
correspond  to  the  pyramidal  cells  of  the  cerebral  cortex. 

The  fourth  layer  in  its  outer  part  has  a  large  number  of  very 
small  granular  cells  between  which  pass  the  descending  neuraxons  of 
the  mitral  cells.  The  nerve-fibers  of  the  olfactory  bulbs  collect  at 
their  posterior  extremities  into  two  bundles:  the  olfactory  tracts. 
The  outer  root-fibers  of  the  olfactory  tract  come  into  relation  with  the 
gyrus  hippocampus,  the  uncus,  and  cornu  ammonis.  The  inner  root- 
fibers  pass  into  the  gyrus  fornicatus. 

Olfactory  Sensations.— The  student,  in  order  to  obtain  clear-cut 
ideas  as  to  the  mechanism  of  the  special  sense  of  smell,  should  bear 


494  PHYSIOLOGY. 

in  mind  the  principle  of  the  arrangement  of  the  olfactory  nerve- 
terminations.  It  is  recalled  that  within  the  mucous  membrane  lie 
the  olfactory  cells.  From  the  peripheral  end  of  each  cell  project 
seven  or  eight  ciliumlike  processes.  These  not  only  project  to  the 
surface  of  the  mucous  membrane,  but  even  to  the  surface  of  the  serous 
fluid  moistening  the  membrane.  Thus,  the  terminal  filaments  are 
placed  in  an  exposed  position  so  that  they  may  very  readily  respond 
to  any  irritant. 

The  proper  stimulus  for  olfactory-nerve  filaments  are  odorous 
substances  which  reach  the  regio  olfactoria  through  the  air  and  must 
be  in  a  volatile  state.  Hence,  olfactory  sensations  are  produced  by 
volatile,  odorous  particles  coming  into  direct  contact  with  the  exposed 
nerve-filaments  during  the  act  of  inspiration.  As  the  regio  olfactoria 
is  located  in  the  highest  portion  of  the  nasal  cavity,  it  becomes  nec- 
essary for  the  individual  to  cause  the  inspired  air  forcibly  to  reach 
this  area.  This  is  accomplished  by  the  act  ordinarily  known  as 
"sniffing." 

During  ordinary  respiration  the  inspired  and  expired  air  courses 
along  close  to  the  septum  and  below  the  inferior  turbinated  bone. 
Should  the  respired  air  be  heavily  charged  with  odorous  particles,  of 
course  some  will  find  their  way  into  the  regio  olfactoria,  as  the  air 
in  this  compartment  is  gradually  changed.  There  will  then  result 
a  sensation  of  smell,  but  it  will  be  faint  and  not  so  sharply  defined 
as  when  the  person  sniffs.  By  the  latter  process  the  air  is  changed 
more  quickly,  and  a  greater  number  of  volatile  particles  irritate  the 
exposed  nerve-endings,  with  the  result  of  a  sharply  defined  sensation. 
The  Sensation  seems  to  occur  at  the  first  moment  of  contact  of  the 
odorous  particles  with  the  mucous  membrane.  The  olfactory  nerve 
tires  very  quickly  when  an  odor  acts  for  a  certain  time;  the  effect 
becomes  weaker  and  weaker  little  by  little,  until  the  odor  is  finally 
unperceived. 

Should  the  free  movement  of  the  air  be  prevented, — as,  for 
example,  when  nasal  catarrh  brings  on  a  tumefaction  of  the  mucous 
membrane  of  the  inferior  turbinate, — the  odorous  impression  cannot 
take  place. 

In  case  many  different  odors  act  simultaneously  upon  one  nasal 
cavity,  the  individual  receives  a  mixed  sensation.  Should  but  two 
odors  act,  the  one  is  perceived  on  the  right  half  of  the  mucous  mem- 
brane of  the  cavity,  the  other  upon  the  left  half. '  There  is  not  a  true 
mixture,  for  the  person  perceives  slightly  the  one  odor  and  slightly 
the  other. 


THE  SENSE  OF  SMELL.  495 

SECONDARY  SENSATION. — The  olfactory  impression  having  been 
made,,  the  secondary  aftersensation  often  remains  for  a  long  time. 
This  is  particularly  the  case  with  strong,  disagreeable  odors.  This 
phenomenon  is  explained  on  the  supposition  that  the  odorous  particles 
remain  in  the  cavity  of  the  nose,  even  in  the  air.  It  is  not  believed 
that  the  manifestation  is  due  to  persistence  of  excitation  of  the  olfac- 
tory nerve-fibers  after  the  stimulus  has  been  removed. 

There  are  subjective  olfactory  sensations  which  are  true  hallucina- 
tions. They  are  often  met  with  in  demented,  hysterical,  or  pregnant 
women.  These  sensations  owe  their  existence  to  some  material  altera- 
tion of  the  nervous  apparatus. 

From  impressions  truly  olfactory  it  becomes  necessary  to  dis- 
tinguish the  gustatory  as  well  as  tactile  or  irritative  sensations  upon 
the  nasal  mucous  membrane.  The  irritation  and  even  pain  produced 
by  the  vapors  of  ammonia  often  lead  it  to  be  improperly  classed  as 
"having  a  bad  odor."  Experimentally,  a  dog  with  both  olfactories 
divided  always  starts  from  the  odor  of  ammonia  or  of  acetic  acid. 
This  is  due  to  painful  stimulation  of  his  Schneiderian  membrane, 
which  gets  its  sensory  nerve-filaments  from  the  second  branch  of  the 
trigeminus. 

Uses. — The  organ  of  smell  represents  an  advance  sentinel  for  the 
functions  of  respiration  and  alimentation.  Among  the  lower  animals 
it  serves  for  the  recognition  of  sex. 

Hyperosmia  and  Anosmia. — Hyperosmia,  or  increased  sensitive- 
ness of  smell,  is  a  common  condition.  It  is  very  apt  to  be  found 
in  hysteria  and  in  many  other  nervous  disorders.  Strychnine  is  one 
of  the  drugs  which  is  capable  of  producing  this  condition  when  it  is 
applied  locally  in  solution. 

Anosmia  is  a  term  used  to  designate  a  condition  which  is  the 
reverse  of  the  one  before  mentioned.  It  may  be  complete,  when  it  is 
usually  congenital.  In  such  a  case  the  olfactory  nerves  are  absent. 
It  is  more  usual,  however,  to  find  the  condition  partial.  Its  causes 
may  be  stenosis  of  the  nasal  cavities,  disease  of  the  olfactory  mucous 
membrane,  or  nervous  diseases.  Strychnine  often  relieves  the  con- 
dition. 

The  Center  of  Smell  lies  in  the  tip  of  the  uncinate  gyrus  upon 
the  inner  surface  of  the  cerebral  hemisphere. 


CHAPTER   XVIII. 

SPECIAL  SENSES  (Continued). 
THE  SENSE  OF  HEARING. 

BY  means  of  the  special  sense  of  hearing  the  individual  gains 
knowledge  of  a  kind  differing  from  the  just-mentioned  senses.  It 
does  not  tell  him  what  is  going  on  in  the  outer  world  by  actual  con- 
tact, as  in  touch  or  taste;  nor  yet  by  particles  of  matter  impinging 
upon  the  exposed  end  of  nerve-filaments.,  as  in  the  sense  of  smell. 
In  the  special  sense  of  hearing  the  impressions  conveyed  to  the 
central  nervous  system  are  produced  by  wavelike  vibrations  in  the 
surrounding  air.  For  the  reception  of  these  vibrations,  so  that 
they  may  be  properly  interpreted  and  the  corresponding  impressions 
conveyed  to  the  brain,  it  becomes  necessary  to  have  a  special  sense- 
organ  :  the  ear. 

The   Ear. 

The  organ  of  hearing  in  its  greatest  simplicity  may  be  repre- 
sented by  a  small  membrane  stretched  like  a  drumhead  over  the  bottom 
of  a  funnel-shaped  tube.  The  tube  opens  upon  the  surface  of  the 
body  so  that  it  is  in  direct  communication  with  the  enveloping  atmos- 
phere. The  membrane  is  so  disposed  that  it  is  readily  thrown  into 
vibrations  when  the  external  air  becomes  undulatory  as  the  result 
of  vibrations  of  some  body.  Its  vibrations  are  communicated  to  an 
inner  vesicle  that  is  filled  with  a  liquid.  The  liquid  is  likewise  thrown 
into  waves  whose  undulations  stimulate  the  ramifications  of  the  audi- 
tory nerve  which  are  spread  out  upon  the  walls  of  the  vibrating  vesicle. 

Anatomy. — The  apparatus  for  hearing  is  composed  of  three  parts : 
external  ear.,  middle  ear,  and  internal  ear. 

EXTERNAL  EAR. — The  external  ear  is  composed  of  the  auricle  and 
external  auditory  meatus. 

The  auricle  has  the  form  of  an  irregularly  shaped  shell.  It  is 
composed  of  yellow,  elastic  cartilage  which  is  covered  over  with  skin. 
From  its  shape  one  might  readily  believe  that  the  function  of  the 
auricle  is  to  collect  and  reflect  sound-waves  into  the  auricle :  that  is, 
to  behave  in  the  capacity  of  an  ear-trumpet.  But  it  is  found  that 
hearing  is  perfectly  normal  in  those  persons  from  whom  the  external 
ear  has  been  removed  by  accident  or  otherwise. 
(496) 


THE  SENSE  OF  HEARING.  497 

The  external  auditory  meatus  and  canal  extend  from  the  concha 
of  the  auricle  to  the  tympanum.  The  canal  is  composed  partly  of 
cartilage  and  partly  of  bone ;  the  bony  portion  belongs  to  the  temporal 
bone.  The  canal  is  lined  by  skin,  which  contains  modified  sebaceous 
and  sudoriferous  glands.  By  the  glands  is  secreted  the  cerumen,  or 
earwax. 

The  internal  end  of  the  auditory  canal  is  bounded  by  an  ellipsoid 
structure  which  is  composed  of  three  layers  of  tissue:  the  tympanic 
membrane. 

The  functions  of  the  external  auditory  canal  are  twofold:  (1) 
to  conduct  waves  of  sound  to  the  membrana  tympani,  and  (2)  to  insure 


Fig.  116. — Diagram  of  the  External  Surface  of  the  Left  Tympanic 
Membrane.     (HENSEN.) 

a,  Head  of  malleus.  6,  Incus,  e,  Joint  between  malleus  and  incus.  Be- 
tween c  and  d  is  the  flaccid  portion  of  the  membrane,  ax,  Axis  of  rotation 
of  ossicles.  The  umbo  is  the  deeply  shaded  part. 

this  membrane,  as  well  as  the  delicate  structure  of  the  middle  ear, 
from  injury. 

MIDDLE  EAR,  OR  TYMPANUM. — The  tympanum  is  a  space  situated 
within  the  substance  of  the  petrous  portion  of  the  temporal  bone.  It 
is  composed  of  two  l>ony  and  four  soft  parts. 

The  two  bony  parts  comprise  the  walls  of  the  cavity,  with  the 
mastoid  cells  and  Eustachian  tube ;  also  the  ossicles  or  bones  of  the  ear. 

The  soft  structures  are:  (1)  the  ligaments  and  muscles  of  the 
little  ossicles,  (2)  the  mucous  membrane  of  the  tympanic  cavity,  (3) 
the  lining  of  the  Eustachian  tube,  and  (4)  the  membrana  tympani 
and  membrane  of  the  round  window. 


498  PHYSIOLOGY. 

In  otitis  media  pus  may  cause  a  disintegration  of  the  mastoid 
cells,  from  which  it  frequently  extends  to  the  membranes  of  the  brain. 

The  cavity  of  the  tympanum  forms  a  dilatation  added  to  the 
auditory  canal.  It  has  an  internal  wall,  an  external  wall,  and  the 
Eustachian  tube.  The  mastoid  cells  communicate  by  a  large  orifice 
with  the  upper,  back  part  of  the  tympanum.  They  are  lined  through- 
out with  a  delicate  mucous  membrane. 

The  external  wall  is  occupied  in  its  greatest  extent  by  an  opening 
which  is  nearly  circular  and  closed  by  the  membrana  tympani.  The 
latter  is  semitransparent,  concave  externally  and  convex  internally. 


Fig.  117. — Tympanic  Membrane  and  Auditory  Ossicles,  seen  from  the 
Tympanic  Cavity.     (IiAifooifi.) 

M,  Manubrium,  or  handle  of  the  malleus.  T,  Insertion  of  the  tensor 
tympani.  h,  Head.  IF,  long  process  of  the  malleus,  or  incus-tooth.  The 
short  (K)  and  the  long  (1)  process.  8,  Plate  of  the  stapes.  Ax  is  the  common 
axis  of  rotation  of  auditory  ossicles.  8,  The  pinion-wheel  arrangement  be- 
tween the  malleus  and  incus. 

To  its  inner  surface  is  attached  the  malleus,  one  of  the  three  ear 
ossicles. 

The  internal  wall  is  convex  and  has  in  its  central  portion  a 
tubercle  known  as  the  promontory.  Its  base  corresponds  to  the  origin 
of  the  cochlea.  The  most  prominent  of  the  grooves  upon  its  surface 
marks  the  position  of  the  nerve  of  Jacobson. 

Above  the  promontory  is  found  the  oval  window.  Its  shape  is 
really  reniform;  it  leads  to  the  vestibule. 

The  round  window  is  situated  just  beneath  the  oval  window.  It 
is  closed  by  a  membrane. 

The  ossicles,  which  form  an  articulated  chain,  reach  from  the 
membrana  tympani  to  the  oval  window.  In  number  they  are  three: 


THE  SENSE  OF  HEARING. 


499 


the  malleus,  or  mallet ;  the  incus,  or  anvil ;  and  the  stapes,  or  stirrup. 
The  three  ossicles  form  a  chain  suspended  across  the  cavity  of  the 
tympanum.  The  handle  of  the  malleus  is  inserted  into  the  tympanic 
membrane;  the  base  of  the  stirrup  is  applied  to  the  oval  window. 
Between  these  two  ossicles  is  suspended  the  incus.  The  ossicles  have 
joints  which  are  lined  with  synovial  membrane;  there  are  present 
suitable  ligaments. 

The  mucous  membrane  of  the  tympanum  is  very  thin,  and  either 
white  or  rose-colored.     It  envelops  the  chain  of  ossicles. 


Fig.    118. — Left   Tympanum   and   Auditory   Ossicles.     (LANDOIS.) 

A.G.,  External  meatus.  M,  Membrana  tympani,  which  is  attached  to  the 
handle  of  the  malleus  (ri)  and  near  its  short  process  (p).  h,  Head  of  the 
malleus,  a,  Incus.  K,  Its  short  process,  with  its  ligament.  I,  Long  process. 
8,  Stapes. 

The  Eustacliian  tube  is  composed  of  a  bony  and  a  cartilaginous 
part.  The  canal  opens  at  the  anterior  upper  part  of  the  tympanum; 
its  pharyngeal  orifice  is  situated  ten  millimeters  behind  the  posterior 
extremity  of  the  nasal  fossa.  The  walls  of  the  tube  open  at  each  move- 
ment of  deglutition  by  reason  of  the  action  of  the  tensor  palati. 

THE  BONY  LABYRINTH,  OR  INTERNAL  EAR. — This  structure  is 
imbedded  within  the  substance  of  the  petrous  portion  of  the  temporal 
bone.  Its  long  axis  lies  in  a  position  parallel  with  that  of  the  bone. 
The  labyrinth  is  composed  of  three  portions :  vestibule,  semicircular 
canals,  and  cochlea. 


500  PHYSIOLOGY. 

The  vestibule  is  an  oval,  irregular  cavity,,  lying  between  the  tym- 
panum and  the  bottom  of  the  internal  auditory  meatus.  The  semi- 
circular canals  open  from  it  posteriorly  and  the  cochlea  opens  from  it 
anteriorly.  Through  its  outer  wall  it  communicates  with  the  tym- 
panum by  the  oval  window.  The  fovea  hemispherica  and  fovea  hemi- 
ettiptica  are  two  depressions  upon  the  inner  and  superior  walls  of 
the  vestibule,  respectively.  They  are  pierced  by  numerous  foramina ; 
through  the  former  pass  the  filaments  of  the  cochlear  branch  of  the 
auditory  nerve;  through  the  latter  foramina  pass  the  branches  of  the 


Fig.  119. — Scheme  of  the  Organ  of  Hearing.     (LANDOIS.) 

-  AG,  External  auditory  meatus.  T,  Tympanic  membrane.  K,  Malleus  with 
its  head  (70,  short  process  (kf),  and  handle  (m).  a,  Incus,  with  its  short 
process  (x)  and  long  process;  the  latter  is  united  to  the  stapes  (s).  P,  Middle 
ear.  o,  Oval  window,  r,  Round  window,  x,  Beginning  of  the  lamina  spiralis 
of  the  cochlea,  pt,  Its  scala  tympani.  vt,  Its  scala  vestibuli.  V,  Vestibule. 
8,  Saccule.  U,  Tubercle.  H,  Semicircular  canals.  TE,  Eustachian  tube. 
The  long  arrow  indicates  the  line  of  traction  of  the  tensor  tympani;  the 
short  curved  one  that  of  the  stapedius. 

-vestibular  branch.  Through  the  latter  also  pass  small  veins  which 
•communicate  with  the  inferior  petrosal  sinus. 

The  semicircular  canals  are  three  in  number.  They  are  located 
above  the  inner  and  back  part  of  the  tympanum.  From  their  location 
they  are  named  superior,  posterior,  and  external.  The  canals  lie  in 
three  distinct  planes :  the  first  two  are  vertical,  but  nearly  at  right 
;angles  to  one  another;  the  last  is  horizontal. 

Each  canal  is  rather  more  than  half  of  a  circle,  and  forms  at  one 
•extremity  a  dilatation  called  the  ampulla.'  The  canals  communicate 


THE  SENSE  OF  HEARING. 


501 


with  the  vestibule  by  five  openings,  one  of  which  belongs  to  both  the 
superior  and  horizontal  canal. 

The  interior  of  the  vestibule  and  semicircular  canals  is  lined  with 
a  delicate  membrane.  The  cavity  formed  by  this  membrane  contains 
a  fluid  of  serous  nature.  It  is  known  as  the  perilymph,  by  reason  of 
its  surrounding  a  secondary  structure,  the  labyrinth.  This  last  struc- 
ture consists  of  a  pair  of  saccules  in  the  vestibule,  and  three  semi- 
circular saccules  whose  form  is  the  same  as  the  osseous  canals  contain- 
ing them.  This  membranous  labyrinth  comprising  the  saccules  just 
mentioned  itself  contains  a  serous  fluid,  the  endolymph. 


Fig.  120.— Scheme  of  the  Labyrinth  and  Terminations  of  the  Auditory 
Nerve.     (LANDOIS.) 

I.  Transverse  section  of  a  turn  of  the  cochlea. 

II.  Ampulla  of  a  semicircular  canal,     a,  p,  Auditory  cells,     p,  Cell  pro- 
vided with  a  fine  hair.    T,  Otoliths. 

III.  Scheme  of  the  human  labyrinth. 

IV.  Scheme  of  a  bird's  labyrinth. 

V.  Scheme  of  a  fish's  labyrinth. 

The  inner  portion  of  the  bony  labyrinth  is  the  cochlea:  so  named 
from  its  resemblance  to  a  shell.  Its  base  is  attached  to  the  internal 
auditory  meatus,  while  its  apex  is  directed  forward  and  outward.  The 
axis  of  the  cochlea  is  nearly  at  right  angles  to  that  of  the  petrous 
portion  of  the  temporal  bone  in  which  it  lies.  The  cochlea  is  a  tube 
of  bone  wound  around  a  central  axis,  each  turn  successively  rising. 
This  bony  tube  is  about  one  and  one-half  inches  long.  Its  beginning 
is  connected  with  the  fore  part  of  the  vestibule  to  produce  the  prom- 
ontory of  the  tympanum;  it  ends  in  a  closed  extremity  called  the 
infundibulum.  The  central  axis  just  spoken  of  is  termed  the  modiolus. 
The  apex  of  the  cochlea  is  often  called  the  cupola. 


502 


PHYSIOLOGY. 


The  bony  canal  is  divided  into  two  passages,  or  scalce,  by  a  septum 
known  as  the  lamina  spiralis,  which  projects  from  the  modiolus.  The 
two  scalaa  communicate  with  one  another  only  at  the  top  of  the  cochlea, 
by  an  opening:  the  hiatus,  or  helicotrema.  That  portion  of  the 
cochlear  canal  that  is  above  the  septum  terminates  in  the  vestibule; 
hence  scala  vestibuli.  The  lower  portion  opens  into  the  tympanum 
through  the  round  window;  hence  scala  tympani. 

The  membranous  portion  of  the  septum,  or  lamina  spiralis,  con- 


St 


Fig.  121. — Section  through  the  Uncoiled  Cochlea  (I)  and  through  the  Terminal 
Nerve  Apparatus  of  the  Cochlea   (II).     (MUNK,  after  Hensen.) 

I.  F.r.,  Round  window.    H,  Helicoterma.    St.,  Stapes. 

II.  Z,  Huschke's  process.       &',  Basilar  membrane,    e,  Corti's  arch,    g,  Sup- 
porting cells,    h,  Cylindrical  cells,    i,  Deiters's  hair-cells,     c,  Membrana  tec- 
toria.    n,  Nerve-fibers,    ri,  Nonmedullated  nerve-fibers. 


sists  of  two  layers:  The  superior  layer  is  the  membrane  of  Corti,  or 
membrana,  tectoria;  the  other  is  the  meriibrana  basilaris.  These  two 
membranes  are  placed  parallel  with  one  another  to  contain  between 
them  the  organ  of  Corti.  The  latter  rests  upon  the  basilar  membrane. 
The  bony  portion  of  the  septum  has,  upon  its  superior  external 
surface,  a  denticulated,  cartilaginous  substance  called  the  lamina  den- 
ticulata.  From  the  superior  surface  of  the  lamina  spiralis,  and  in- 
ternal to  the  lamina  denticulata,  exists  a  delicate  membrane,  the 


THE  SENSE  OF  HEARING. 


503 


membrane  of  Reissner.  This  membrane  divides  the  scala  vestibuli 
into  two  passageways,  one  of  which  is  the  ductus  cochlearis.  It  con- 
tains the  essential  portion  of  the  auditory  apparatus  of  the  cochlea: 
the  organ  of  Corti.  It  forms  part  of  the  membranous  labyrinth. 

The  membranous  labyrinth  is  a  closed  sac  consisting  of  semi- 
circular canals,  a  vestibular  portion,  and  the  membranous  part  of  the 
lamina  spiralis.  The  vestibular  portion  consists  of  an  expanded  body, 
the  utricle,  and  a  smaller  body,  the  saccule.  Within  these  compart- 
ments are  two  calcareous  bodies:  the  otolitlis.  The  vestibular  fila- 


Fig.  122. — Section  of  the  Ductus  Cochlearis  and  the  Organ  of  Corti. 
(After  LANDOIS.) 

N,  Cochlear  nerve.  K,  Inner,  and  P,  outer,  hair-cells,  n,  Nerve-fibrils 
terminating  in  P.  a,  a,  Supporting  cells,  d,  Cells  in  the  sulcus  spiralis. 
z,  Inner  rod  of  Corti.  Mb,  Corti,  membrane  of  Corti,  or  the  membrana 
tectoria.  o,  The  membrana  reticularis.  H,  G,  Cells  filling  up  the  space  near 
the  outer  wall. 

ments  of  the  cochlear  nerve  are  distributed  to  the  ampullae,  utricle,  and 
saccule.  In  the  first  the  fibers  terminate  in  elevations  called  cristaz 
acusticce;  in  the  last  two  they  end  as  oval  plates, — maculae, — colored 
by  yellow  pigment. 

Organ  •  of  Corti. — The  organ  of  Corti  contains  the  following 
elements : — 

1.  Arches  of  Corti. — They  are  formed  of  an  internal  and  ex- 
ternal pillar  whose  pedestals  rest  upon  the  basilar  membrane.  The 
arches  intercept  the  canal  of  Corti. 


504  PHYSIOLOGY. 

2.  Internal  Auditory  Cells. — Inward  from  the  internal  pillar  of 
Corti  is  found  a  layer  of  auditory  cells.     These  cells  contain  nuclei, 
while  their  superior  extremities  terminate  in  a  plateau  having  long 
ciliated  prolongations;   their  inferior  extremities  are  in  relation  with 
the   basilar   membrane   and   axis-cylinder   of   the   terminal   cochlear 
branches  of  the  auditory  nerve. 

3.  A  Granular  Layer  composed  of  rounded  cells. 

4-  Cells  in  the  sulcus  spiralis  which  are  cubical  in  shape. 

5.  The  External  Auditory  Cells,  whose  structure  and  arrangement 
is  very  similar  to  the  internal  cells  just  mentioned. 

6.  The  Cells  of  Deiters,  Hensen,  and  Claudius,  which  make  a 
prominence  upon  the  interior  of  the  cochlear  canal. 

7.  Reticular  Membrane. — The  membrana  reticularis   is   formed 
by  the  superior  extremity  of  the  cells  of  Deiters.     It  possesses  lacunae 
which  allow  the  passage  of  cilia  of  the  cells. 

8.  The  Membrane  of  Corti,  or  membrana  tectoria,  is  a  soft,  thick 
membrane  which  covers  the  spiral  groove  and  organ  of  Corti.     Be- 
neath it  adheres  to  the  cilia  of  the  auditory  cells. 

Auditory  Nerve. — The  auditory  nerve  consists  of  two  parts :  the 
cochlear,  the  hearing  part,  and  the  vestibular,  the  tonus  part.  The 
cochlear  part  arises  in  the  spiral  ganglion  of  the  cochlea,  and,  like  a 
posterior  root  ganglion,  sends  a  branch  to  the  auditory  cells  in  the 
organ  of  Corti  and  a  central  branch  to  the  cochlear  nucleus  in  the 
medulla.  The  cochlear  nucleus  consists  of  two  parts:  the  accessory 
nucleus  and  the  tuberculum  acusticum.  Hence  the  first  neuron  ex- 
tends from  the  spiral  ganglion  to  the  cochlear  nucleus;  then  the 
two  divisions  of  the  cochlear  nucleus — the  accessory  nucleus  and 
tuberculum  acusticum — send  out  neuraxons  to  the  superior  olive ;  here 
they  are  second  neurons.  The  superior  olive  sends  out  neuraxons  to 
the  lateral  fillet ;  here  the  third  neuraxons  make  up  chiefly  the  lateral- 
fillet  fibers.  These  go  to  the  posterior  quadrigemina  and  finally  are 
connected  with  the  seat  of  hearing  in  the  first  temporal  convolution. 

The  vestibular  root  arises  in  Scarpa's  ganglion-cells  of  the  laby- 
rinth and  goes  to  the  auditory  nucleus.  From  here  neuraxons  go  up 
by  the  restiform  body  to  the  nucleus  of  the  roof  (nucleus  fastigii) 
and  nucleus  globosus  of  the  opposite  side  of  the  cerebellum. 

The  cochlear  nerve  is  the  nerve  concerned  in  hearing. 

The  vestibular  nerve  is  the  nerve  concerned  in  equilibration.  It 
does  not  have  anything  to  do  with  hearing. 

The  functions  of  the  auricle  and  external  auditory  meatus  and 
canal  have  been  mentioned  above.  The  membrana  tympani,  like  all 


THE  SENSE  OF  HEARING. 


505 


elastic  and  stretched  bodies,  enters  into  vibrations  when  it  is  directly 
struck  or  when  a  body  produces  a  sound  that  is  capable  of  setting  this 
membrane  into  a  vibration  of  unison.  The  contact  of  the  hammer  pos- 
sesses the  role  of  a  damper ;  it  arrests  the  vibrations  of  the  membrane 
and  to  a  certain  measure  makes  the  different  vibrations  follow  each 
other  in  a  regular,  noninterfering  manner.  It  is  probably  a  function 
of  the  tensor  tympani  to  relax  the  membrane  in  case  of  violent  noises, 
as  with  cannon-shots.  By  this  means  rupture  of  the  membrane  is 
prevented.  The  vibrations  of  the  membrana  tympani  are  transmitted 
to  the  internal  ear  by  the  chain  of  ossicles  as  well  as  by  the  air  in 
the  middle  ear. 


Fig.  123. — I.  The  Mechanics  of  the  Auditory  Ossicles.     (After  HELMHOLTZ.) 
II.  Section  of  the  Middle  Ear.     (MuNK,  after  Hensen.) 

I.  a,   Malleus,     h,   Incus,     am,  Long  process   of  incus,     s,   Stapes.     The 
arrows  show  the  direction  of  motion. 

II.  G,  External  auditory  canal.    M.t.,  Membrana  tympani.    C,  Tympanum. 
H,  Malleus.      L.S.,  Superior  ligament.     S,  Stapes. 

The  Eustachian  tube  is  closed  at  its  pharyngeal  end  except  during 
deglutition.  Thus,  if  one  closes  the  mouth  and  nose  and  then  expires 
forcibly  at  the  moment  of  deglutition,  there  is  heard  a  dry  crackling 
in  the  ear  from  the  entrance  of  air  into  the  middle  ear  with  depression 
of  the  tympanum.  The  tube  thus  acts  as  a  medium  whereby  there  is 
established  an  equilibrium  between  the  intratympanic  pressure  and 
the  pressure  of  the  atmosphere.  Should  the  pressure  be  not  equal 
upon  each  side,  as  in  closure  of  the  Eustachian  tube,  then  the  vibra- 
tions of  the  membrane  are  made  with  difficulty.  In  making  descent 


506  PHYSIOLOGY. 

in  a  deep  mine  where  the  atmosphere  is  considerably  more  dense  than 
that  on  the  surface,  the  uninitiated  is  instructed  to  swallow  every 
few  minutes.  By  so  doing  he  maintains  an  equable  pressure  upon 
both  sides  of  the  membrana  tympani. 

It  will  be  recalled  by  the  student  that  all  of  the  spaces  and  com- 
partments of  the  internal  ear.,  or  labyrinth,  are  filled  with  fluid,  and 
that  in  this  fluid  float  saccules  also  containing  serous  fluid.  So 
intimately  are  all  of  the  parts  of  the  labyrinth  associated  that  any 
vibration  of  its  contained  fluid  at  one  part  is  promptly  propagated  to 
every  other  portion.  The  vibrations  of  the  fluid  striking  upon  the 
tiny  nerve-filaments  act  as  stimulants  whose  impressions  are  carried 
to  the  center  of  hearing,  where  the  impressions  are  recognized  as 
sound. 

To  epitomize :  The  sonorous  waves  collected  by  the  auricle  to  pass 
through  the  external  auditory  meatus  and  along  its  canal  strike  the 
surface  of  the  membrane  of  the  tympanum.  It  becomes  tense,  vibrates 
in  unison,  and  then  communicates  its  vibrations  through  the  ossicles 
and  contained  air  in  the  tympanum  to  the  oval  window. 

From  here  the  vibrations  are  carried  over  the  vestibule,  semicircu- 
lar canals,  and  labyrinth  to  the  perilymph.  From  this  last  the  vibra- 
tions are  transmitted  through  the  membranous  walls  of  the  sacculus  to 
the  endolymph.  Vibrations  also  pass  from  the  vestibule  to  the  scala 
vestibuli  of  the  cochlea,  and,  descending  the  scala  tympani,  end  as  an 
impulse  against  the  membrane  of  the  round  window. 

Most  of  the  organs  of  special  sense  contain  a  "specially  modified 
epithelium"  for  the  reception  of  the  particular  kind  of  stimulus 
peculiar  to  each  other.  Nor  is  the  sense  of  hearing  different  from 
the  others.  It  also  has  its  tissues  representing  "  specially  modified 
epithelium"  in  which  lie  the  terminal  filaments  of  the  auditory  nerve. 
These  tissues  are  so  constituted  that  they  receive  the  "waves  of  sound" 
which  generate  in  the  auditory  nerve :  auditory  impulses.  These  last, 
when  conveyed  to  the  brain,  are  developed  into  auditory  sensations. 

The  vibrations  of  elastic  bodies  produce  condensation  and  rare- 
faction of  the  enveloping  atmosphere.  That  is,  there  are  developed 
waves  whose  particles  vibrate  longitudinally.  These  waves  are  usually 
spoken  of  as  sound-waves. 

Normally,  then,  the  auditory  nerve  may  be  stimulated  by  sonorous 
vibrations  which  set  into  motion  the  end-filaments  of  the  acoustic 
nerve.  The  filaments  are  distributed  over  the  inner  surface  of  the 
membranous  labyrinth,  upon  the  membranous  expansions  of  the  coch- 
lea, and  in  the  semicircular  canals.  The  excitement  of  the  filaments 


THE  SENSE  OF  HEARING.  507 

is  really  mechanical  in  nature,  due  to  the  wavelike  motion  of  the 
serous  fluid  of  the  membranous  labyrinth. 

Conduction  through  the  bones  of  the  head  occurs  very  readily 
when  the  vibrating  solid  body  is  applied  directly  to  some  part  of  the 
head.  This  is  exemplified  by  placing  a  tuning  fork  upon  the  head, 
or  by  the  striking  together  of  stones  when  the  head  is  submerged 
beneath  the  surface  of  water. 

It  is  common  to  divide  auditory  stimuli  into  those  which  are 
caused  by  noises  and  those  caused  by  musical  sounds.  It  is  a  feature 
peculiar  to  musical  sounds  that  the  vibrations  which  form  them  are 
periodical  and  that  they  recur  at  regular  intervals.  When  neither 
of  these  two  conditions  is  present,  there  results  a  noise.  From  the 
sensory  impulses  to  which  the  several  vibrations  give  rise  are  generated 
our  sensations  of  noise  or  of  sound. 

To  produce  a  sensation  certain  conditions  in  the  excitation  of 
the  auditory  nerve  are  necessary. 

The  sound-wave  must  exist  for  a  certain  length  of  time ;  it  must 
not  be  less  than  1/30  nor  greater  than  1/400oo  second.  In  the  piano 
the  lowest  base  (C,  33  vibrations)  and  the  highest  treble  (C,  4224: 
vibrations)  exist.  A  certain  number  of  impulses  must  be  made  within 
a  given  interval  of  time  to  excite  a  sensation  of  tone.  The  lower 
limit  is  about  30  vibrations,  the  upper  limit  about  40,000,  per  second. 
Visual  sensations  separated  by  less  than  a  tenth  of  a  second  are  fused, 
but  auditory  sensations  separated  by  1/134  second  remain  distinct. 

Theory  of  Hearing. — If  you  sing  a  note  into  a  piano,  the  cords 
of  the  piano  tuned  for  this  note  only  respond.  Now  the  basilar  mem- 
brane is  supposed,  like  a  harp,  to  represent  a  series  of  cords  which, 
like  the  piano-strings,  respond  to  the  sounds  striking  them.  This 
membrana  basilar  is  is  striated  in  a  radiating  direction,  and  these 
striations  increase  as  it  ascends  toward  the  helicotrema.  Unlike  the 
harp,  the  cords  are  joined  together  by  their  edges;  but,  as  they  are 
stretched  only  in  a  radiating  direction,  they  can  vibrate  as  though  they 
were  separate  cords.  Now,  the  cords  are  very  short,  being  at  most  not 
over  1/12  inch  in  length ;  so  that  they  would  be  expected  only  to  vibrate 
for  high  sounds;  but  it  must  be  remembered  that  these  cords  are 
weighted  with  the  arches  and  cells  of  Corti,  which  lower  their  sound. 
Hence  we  have  a  series  of  cords  in  the  basilar  membrane  vibrating 
separately  to  musical  sounds.  We  know  that  there  is  in  man  about 
3000  arches  of  Corti,  and  as  at  least  two  of  the  cords  correspond  to  an 
arch  of  Corti,  we  have  6000  cords.  Now,  the  scale  of  musical  sounds 
extends  to  seven  octaves,  and  we  have  400  arches  of  Corti  to  1  octave. 


508  PHYSIOLOGY. 

In  1  octave  there  are  12  semitones,  and  we  have  66  cords  correspond- 
ing to  a  semitone ;  so  that  we  have  sufficient  cords  to  vibrate  in  unison 
with  all  possible  musical  sounds. 

When  the  sound-waves  vibrate  the  cells  of  Corti  they  make  the 
terminal  filaments  of  the  cochlear  nerve  vibrate,  because  they  are  in 
relation  with  the  cells  of  Corti.  The  differentiation  of  sounds  takes 
place  in  the  brain. 

Binaural  Audition. — The  hearing  of  a  single  sound  with  both  ears 
may  be  due  to  habit  or  to  the  connection  in  the  nerve-centers  of  the 
fibers  connected  with  both  ears.  Undoubtedly  binaural  audition  facili- 
tates our  knowledge  of  the  direction  of  sound,  since  each  ear  has  its 
own  axis  and  direction. 

The  semicircular  canals  are,  through  the  vestibular  nerve  and  the 
cerebellum,  the  most  important  agents  in  the  preservation  of  equi- 
librium. When  in  a  pigeon  the  horizontal  canals  are  divided  the  head 
moves  from  left  to  right  and  from  right  to  left,  with  nystagmus  and  a 
tendency  to  revolve  on  its  vertical  axis.  When  the  inferior  vertical  or 
posterior  canals  are  divided,  the  head  oscillates  from  front  to  rear; 
the  animal  has  a  tendency  to  fall  backward.  A  section  of  the  superior 
vertical  canal  causes  the  head  to  oscillate  from  front  to  rear,  with  a 
tendency  to  fall  forward.  A  section  of  all  the  canals  is  followed  by 
contortions  of  the  most  bizarre  nature.  After  a  destruction  of  all  the 
canals  the  animal  cannot  maintain  his  equilibrium. 

Similar  phenomena  have  been  observed  in  man  in  disease  of  the 
semicircular  canals,  known  as  Meniere's  vertigo.  In  the  fixed  position 
of  the  head  there  is  equilibrium.,  but  with  each  movement  the  tension 
of  the  liquid  in  the  ampulla  changes  and  irritates  the  vestibular  nerve. 
These  ampullae  and  canals  are  then  sensory  organs,  and  give  the  animal 
an  idea  of  the  position  of  his  head  in  space.  Now,  as  the  canals  are 
at  right  angles  to  each  other  according  to  the  three  dimensions  in 
space,  their  section  makes  the  animal  unable  to  know  the  position  of 
his  head  and  thus  produces  vertigo.  Cyon's  theory  is  that  the  semi- 
circular canals  give  us  a  series  of  unconscious  sensations  as  to  the 
position  of  our  heads  in  space. 


CHAPTER   XIX. 

SPECIAL   SENSES    (Concluded). 
VISION. 

THOSE  bodies  are  said  to  be  luminous  which  especially  affect  the 
organ  of  vis.ion.  Some  are  luminous  in  themselves,  others  become 
so  by  reflection.  Since  there  is  no  direct  contact  between  the  visual 
apparatus  and  the  object  which  makes  the  impression,  and  since  the 
distance  which  separates  them  is  often  infinite,  it  is  impossible  not 
to  admit  the  existence  of  a  particular  intervening  agent  between  the 
center  of  radiation  and  the  eye.  This  agent  is  ether. 

How  Does  Light  Transmit  Itself? — The  accepted  theory  to-day 
with  regard  to  its  propagation  is  the  undulatory,  or  wave-,,  theory. 
Its  doctrines  make  light,  like  heat  and  sound,  a  mode  of  motion. 

A  luminous  body  is  one  whose  particles  are  in  a  state  of  vibration. 
That  they  may  give  rise  to  a  luminous  impression  it  is  necessary  that 
they  be  transmitted  to  the  eye.  Ordinarily  the  atmospheric  air  is  the 
usual  medium  for  the  transmission  of  the  vibrations  of  a  sounding 
body  to  our  ears.  However,  a  luminous  body  does  not  become  invisible 
in  a  vacuum,  as  does  a  sounding  body  become  inaudible.  Hence,  there 
must  be  supposed  the  existence  of  a  highly  elastic  medium  that  per- 
vades all  space  and  all  bodies.  To  this  especial  medium  luminous 
bodies  communicate  their  vibrations  to  be  transmitted  with  enormous 
velocity.  This  medium  is  known  to  physicists  as  ether. 

Suppose  a  luminous  body  isolated  in  a  gas  or  suspended  in  a 
vacuum ;  it  will  be  visible  in  all  directions.  Imagine,  also,  a  point  of 
space  lighted  up  by  its  radiations.  The  line  which  joins  this  point 
to  one  of  the  elements  of  the  luminous  body  represents  the  direction  of 
a  ray  of  light.  So  long  as  no  obstruction  intervenes  the  ray  of  light 
pursues  an  even,  straight  course.  Should,  however,  a  mirror  inter- 
cept its  path,  the  greater  portion  of  it  will  be  bent  out  of  its  regular 
course.  That  is,  it  is  reflected.  In  all  cases  of  reflection  it  is  well  to 
remember  that  "the  angle  of  reflection  always  equals  the  angle  of  in- 
cidence." 

Again,  the  passage  of  light  through  transparent  media  of  various 
densities  presents  peculiarities:  its  straight  course  is  modified — 
broken.  To  convey  a  conception  of  this  phenomenon  the  term  re- 
fraction is  used. 

(509) 


510  PHYSIOLOGY. 

Visual  Apparatus. 

The  organ  of  sight,  the  eye,  is  constructed  upon  the  principles  of 
the  camera  obscura.  In  the  latter  the  collecting  lens  unites  the  light 
impressions  at  the  back  of  the  apparatus  to  form  upon  the  ground- 
glass  plate  a  diminished  and  reversed  image  of  external  objects. 

Structure. — The  eye  is  composed  of  three  concentric  coats  (scle- 
rotic, choroid,  and  retina),  the  aqueous  and  vitreous  humors,,  and  the 
crystalline  lens. 


Fig.  124. — Diagram  of  a  Horizontal  Section  through  the  Human  Eye.     (YEO.) 

1,  Cornea.  2,  Sclerotic.  3,  Choroid.  4,  Ciliary  processes.  5,  Suspensory 
ligament  of  lens.  6,  So-called  posterior  chamber  between  iris  and  lens.  7, 
Iris.  8,  Optic  nerve.  8',  Entrance  of  cerebral  artery  of  retina.  8",  Central 
depression  of  retina,  or  yellow  spot.  9,  Anterior  limit  of  retina.  10,  Hyaline 
membrane.  11,  Aqueous  chamber.  12,  Crystalline  lens.  13,  Vitreous  humor. 
14,  Circular  venous  sinus  which  lies  around  the  cornea,  a-a,  Antero-posterior 
axis  of  bulb.  b-&,  Transverse  axis  of  bulb. 

The  first,  or  outside,  coat  of  the  eye  is  opaque  in  all  of  its  parts 
except  a  small  anterior  segment.  This  area,  which  is  about  one-sixth 
of  the  entire  circumference,  is  perfectly  transparent.  The  dense 
opaque  part  is  known  as  the  sclerotic;  the  transparent  portion  is  the 
cornea,  which  is  the  most  anterior  portion  of  the  sclerotic. 

THE  SCLEROTIC  is  composed  of  fibrous  connective  tissues  whose 
bundles  are  woven  together  both  circularly  and  longitudinally.  It 
contains  a  few  blood-vessels  in  the  form  of  a  wide-meshed  capillary 
plexus. 


VISION.  oil 

THE  CORNEA  represents  a  cap  of  a  smaller  sphere  attached  to  the 
larger,  sclerotic  sphere.  It  is  transparent  and  resembles  very  much 
a  watch-glass  in  form.  The  cornea  is  thicker  at  its  periphery  than  in 
its  center.  This  little,  transparent  window  is  composed  of  five  dif- 
ferent layers. 

In  the  third  layer  the  connective-tissue  fibers  are  arranged  in  thin 
plates.  Between  the  plates  are  series  of  spaces  which  communicate 
with  each  other  and  which  are  lined  with  endothelium.  These — 
called  the  lymph-spaces — communicate  with  the  lymphatics  of  the 
conjunctiva. 

Within,  but  not  quite  filling,  the  lymph-spaces  lie  the  fixed 
corpuscles  of  the  cornea,  which  are  connective-tissue  corpuscles.  Leu- 
cocytes also  pass  into  these  lymph-spaces.  The  membrane  of  Descemet 
constitutes  the  fourth  layer  from  the  outside. 

Long  and  short  ciliary  nerves  supply  branches  to  the  cornea. 
They  penetrate  it  from  the  periphery,  divide,  and  subdivide,  some  of 
them  terminating  in  the  corneal  corpuscles.  Others  end  within  small 
knobs  placed  between  the  deep  and  middle  epithelial  cells.  The 
blood-vessels  are  at  the  margin  of  the  cornea,  there  being  none  within 
its  substance. 

THE  CHOROID  is  the  vascular  coat  of  the  eye,  containing  some 
pigment-granules.  Its  external  layer  is  composed  principally  of 
blood-vessels  and  nerves.  Between  the  vessels  are  found  numerous 
stellate  pigment-cells  which  form  a  fibrous  network.  That  portion 
of  the  internal  surface  which  is  joined  to  the  retina  also  contains 
pigment-cells.  Posteriorly  it  is  penetrated  by  the  optic  nerve;  an- 
teriorly it  is  continuous  with  the  ciliary  processes  and  iris.  The 
choroid  lies  beneath  the  sclerotic,  covering  the  posterior  five-sixths  of 
the  eyeball. 

The  ciliary  arteries  furnish  an  abundant  supply  of  blood  to  this 
coat  of  the  eye.  The  ciliary  veins  collect  the  deoxygenated  blood. 
They  perforate  the  sclerotic  just  behind  the  equator  of  the  globe  of 
the  eye. 

Iris. — The  anterior  one-sixth  of  the  choroid  is  composed  of  a 
muscular  curtain  known  as  the  iris.  It  is  practically  a  diaphragm 
with  a  central  opening,  called  the  pupil.  The  iris  is  separated  from 
the  cornea  by  the  anterior  chamber  of  the  eye. 

The  musculature  of  the  iris  comprises  both  circular  and  radiating 
fibers.  The  pupil  is  made  smaller  by  contraction  of  its  circular  fibers. 
These  belong  to  the  smooth  type  of  muscle-fibers  and  are  innervated 
by  the  oculomotor  through  the  medium  of  its  ciliary  branches. 


512  PHYSIOLOGY. 

The  pupil  enlarges  through  contraction  of  the  radiating  fibers 
of  the  iris.  It  is  innervated  by  the  ciliary  branches  derived  from 
the  great  sympathetic.  Sensory  nerves  are  present,  coming  from  the 
first  branch  of  the  fifth,,  or  trigeminus. 

Hence,  stimulation  of  the  oculomotor  and  trigeminus,  as  well  as 
cutting  the  sympathetic  nerve  in  the  neck,  produces  contraction  of  the 
pupil.  Irritation  of  the  sympathetic  causes  the  pupil  to  dilate.  The 
normal  contraction  and  dilatation  of  the  pupil  are  reflex  movements 
that  are  caused  by  the  rays  of  a  very  strong  or  very  faint  light  striking 
the  retina.  From  the  retina  the  impression  is  conveyed  to  the  an- 
terior corpora  quadrigemina  and  then  to  the  oculomotor  nucleus  and 
its  nerve  to  the  iris.  It  is  not  due  to  the  direct  action  of  light  upon  the 
iris  itself. 

The  iris  is  composed  of  several  layers,  in  the  posterior  one  of 
which  is  the  pigmentary  epithelium.  In  brunettes  the  color  is  due 
to  pigmented  connective-tissue  corpuscles.  The  artery  and  veins  of 
the  iris  lie  at  its  periphery. 

In  the  ciliary  portion  of  the  choroid  is  located  the  ciliary  muscle: 
the  muscle  of  accommodation.  It  contains  two  layers :  one  radiating, 
the  other  circular. 

The  ciliary  processes,  about  sixty  in  number,  are  conical  bodies 
which  project  inward  from  the  ciliary  ring  into  the  posterior  chamber 
of  the  eye.  They  are  the  most  important  part  of  the  choroid  coat. 

Uses. — By  reason  of  its  vascularity  the  choroid  is  destined  to 
nourish  the  all-important  and  underlying  retina.  By  reason  of  its 
elasticity  and  contained  musculature  the.  choroid  maintains  intra- 
ocular pressure.  The  pigment  of  the  choroid  is  believed  to  serve  a 
dioptric  purpose :  that  of  absorbing  the  superfluous  rays  of  light 
which  pass  through  the  eyeball  on  their  way  to  the  retina.  Their 
absorption  prevents  dazzling  and  interference  with  vision. 

THE  EETIXA. — The  optic  nerve  pierces  the  eye  a  little  to  the 
inner  side  of  the  center  of  the  eyeball.  It  soon  divides  into  numerous 
small  bundles  of  ultimate  fibers  which  appear  to  spread  themselves  out 
so  as  to  inosculate  with  one  another  and  thus  form  a  network.  It 
is  this  plexus  which  constitutes  the  inner  layer  of  the  retina.  The 
most  anterior  portion  of  the  retina  is  the  ora  serrata. 

The  retina  is  composed  of  two  main  portions:  the  pigmentary 
membrane  and  the  terminal  elements  of  the  optic  nerve. 

The  pigmentary  layer  has  been  called  the  uvea.  It  covers  the 
entire  inner  surface  of  the  ciliary  processes,  the  iris,  and  the  choroid. 
It  is  composed  of  a  layer  of  nucleated,  hexagonal  pigment-cells. 


VISION.  513 

* 

The  nervous  layer  of  the  retina  is  composed  principally  of  the 
terminal  nerve-elements  of  the  optic  nerve.  Externally,  it  is  coated 
with  a  pigment-layer;  internally,  it  is  lined  with  a  homogeneous, 
transparent  structure,  the  hyaloid  membrane. 

Histological  Structure. — The  histological  structure  of  the  retina 
is  very  complicated.  The  retina  is  really  an  outward  expansion  of  the 
original  f  orebrain.  The  retina  is  usually  divided  into  eight  layers : — 

1.  The  layer  of  nerve-fibers. 

2.  The  layer  of  ganglionic  cells. 

3.  The  inner  molecular  layer. 

4.  The  inner  nuclear  layer. 

5.  The  outer  molecular  layer. 

6.  The  outer  nuclear  layer. 

7.  The  layer  of  rods  and  cones. 

8.  The  hexagonal  pigment-layer. 

The  first  layer  consists  of  neuraxons  from  the  ganglionic  cells 
of  the  second  layer.  The  second  layer  consists  of  a  lot  of  multipolar 
nerve-cells,  and  their  neuraxons  run  inward  to  form  most  of  the  fibers 
of  the  optic  nerve.  The  dendrons  of  these  multipolar  cells  are 
branched  and  terminate  in  the  inner  molecular  layer,  of  which  this 
third  layer  is  chiefly  composed.  The  fourth  inner  nuclear  layer  is 
made  up  chiefly  of  round  and  oval  cells  with  a  peripheral  neuraxon 
and  a  central  neuraxon. 

The  peripheral  neuraxon  arborizes  around  the  dendrons  of  a  gan- 
glionic cell  in  the  inner  molecular  layer. 

The  fifth  outer  molecular  layer  is  made  up  of  the  arborizations  of 
the  neuraxons  of  the  visual  cells  of  the  outer  nuclear  layer. 

The  sixth  layer,  the  outer  nuclear  layer,  is  the  layer  of  bipolar 
visual  cells.  Their  central  neuraxons  end  in  arborizations  in  the  outer 
molecular  layer  about  the  dendrons  of  the  bipolar  cells  of  the  inner 
nuclear  layer.  The  peripheral  processes  of  these  cells  are  the  rods 
and  cones  of  the  retina,  which  are  similar  to  the  dendrons  of  other 
nerve-cells. 

The  seventh  layer  of  rods  and  cones  are  the  dendrons  of  the  visual 
cells. 

The  eighth  layer  is  the  pigment-layer  of  the  retina. 

The  retina  is  essentially  formed  by  a  number  of  nerve-cell  chains, 
the  elements  of  which  are  arranged  in  three  series  from  without  in. 
The  first  is  the  rod  and  cone;  the  second  is  the  bipolar  cell, which 
interlaces  with  the  peripheral  dendrons  of  the  ganglionic  cells.  The 
third  element  is  the  ganglion-cell. 


514 


PHYSIOLOGY. 


The  optic  tract  arises  in  the  retinal  cells,  which  is  its  trophic  cen- 
ter. These  retinal  cells  send  in  fibers  which  arborize  around  the  cells 
of  the  anterior  corpora  quadrigemina,  pulvinar,  and  the  lateral  corpus 
geniculatum.  Now,  from  the  lateral  corpus  geniculatum  and  pulvinar 
we  have  a  second  set  of  neuraxons  running  to  the  occipital  cortex,  the 
center  of  vision.  Here  the  lateral  corpus  geniculatum  and  pulvinar 
are  the  relay  centers  in  the  path  of  visual  impulses. 


Fig.  125. — Vertical  Section  of  Human  Retina.     (LANDOIS.) 

a,  Rods  and  cones.  6,  External  limiting  membrane,  c,  External  nu- 
clear layer,  e,  External  granular  layer,  f,  Internal  nuclear  layer,  g,  In- 
ternal granular  layer,  j,  Internal  limiting  membrane. 

Rods  and  Cones. — The  rods  are  cylindrical  bodies,  each  of  which 
ends  externally  in  a  truncated,  flattened  extremity.  The  cones,  as 
their  name  indicates,  are  conical  bodies. 

It  has  been  demonstrated  that  the  rods  and  cones  consist  of  two 
segments,  or  limbs,  which  are  composed  of  -fibers  and  granular  matter. 
Continued  strong  light  produces  swelling  of  the  rods;  they  shrink 
again  in  darkness.  The  rods  and  cones  show  that  their  outer,  granular 


VISION.  515 

matter  breaks  up  into  transverse  plates.  The  inner  segments  are  stri- 
ated by  reason  of  fibers  prolonged  into  them  from  the  external  limit- 
ing membrane. 

Number. — In  man  and  mammals  the  number  of  rods  far  exceeds 
that  of  the  cones.  The  reverse  is  true  in  birds. 

Macula  Lutea. — The  yellow  spot  of  Soemmering  is  an  oval  depres- 
sion in  the  center  of  the  retina.  It  measures  one-twentieth  of  an  inch 
across  and  is  one-tenth  of  an  inch  to  the  outer  side  of  the  point  of 
entrance  of  the  optic  nerve.  Its  center  is  the  fovea  centralis.  In  the 
fovea  there  are  no  rods;  cones  only  are  present,  and  these  are  longer 
and  narrower  than  those  of  the  other  parts  of  the  retina. 

When  the  optic  nerve  penetrates  the  eye  it  projects  somewhat  be- 
yond the  inner  surface  of  the  eyeball  as  a  papilla.  In  this  papilla 
there  are  none  of  the  essential  nerve-elements  of  the  retina,  so  that 
rays  of  light  cannot  be  perceived  by  this  particular  area;  hence  the 
name  of  blind  spot. 

CRYSTALLINE  LENS. — The  lens  is  a  biconvex,  solid,  transparent 
body,  located  behind  the  iris  and  in  front  of  the  vitreous  body.  Its 
greater  convexity  is  on  the  posterior  surface.  The  transverse  and 
vertical  diameters  are  about  one-third  of  an  inch ;  the  antero-posterior 
one  is  but  one-sixth. 

The  lens  is  enveloped  in  a  capsule  of  fibrous  membrane.  The 
substance  of  the  lens  is  made  up  of  fibers  which  were  originally  cells. 
The  fibers  are  in  concentric  layers  traceable  from  the  posterior  sur- 
face to  the  anterior.  The  suspensory  ligament  of  the  lens  is  derived 
from  the  hyaloid  membrane  of  the  vitreous  body. 

Cataract. — Normally  the  lens  is  transparent.  When  it  becomes 
opaque  for  any  reason  then  there  results  the  condition  known  as 
cataract.  This  condition  is  artificially  produced  in  frogs  by  the  in- 
jection of  grape-sugar.  Cataract  in  diabetes  is  from  the  same  cause. 

AQUEOUS  HUMOR. — This  fluid  contains  about  2  per  cent,  of  solids, 
chiefly  in  the  form  of  sodium  chloride.  It  occupies  the  anterior 
chamber  in  the  space  back  of  the  cornea  and  in  front  of  the  iris.  The 
so-called  posterior  chamber  lies  between  the  back  of  the  iris  and  in 
front  of  the  lens. 

VITREOUS  HUMOR. — The  vitreous  humor  is  a  gelatinous  body 
which  is  held  in  its  position  posterior  to  the  crystalline  lens  by  the 
hyaloid  membrane.  At  the  ora  serrata  the  membrane  splits  into  two 
layers :  one,  the  hyaloid  membrane  proper,  passes  over  the  front  of  the 
vitreous  body ;  the  other,  a  fibrous  structure,  is  much  firmer  than  the 
true  hyaloid.  It  extends  over  the  ciliary  processes  to  be  attached  to 


516  PHYSIOLOGY. 

the  capsule  of  the  lens,  forming  for  it  a  suspensory  apparatus:  the 
zonule  of  Zinn. 

The  lymphatic  canal  of  Petit  is  formed  by  the  splitting  of  the 
two  layers  of  the  hyaloid  membrane. 

In  the  center  of  the  vitreous  body  is  the  canal  of  Stilling.  Dur- 
ing foetal  life  it  transmitted  the  artery  of  Zinn  to  the  back  of  the 
capsule  of  the  lens. 

When  by  ulceration  of  the  cornea  or  accident  the  aqueous  humor 
escapes,  it  is  found  to  be  regenerated  very  rapidly. 

The  secretion  of  the  aqueous  humor  has  been  studied  by  fluorescin 
instilled  into  the  fluids  of  the  eyeball.  It  has  been  found  that  the 
humor  is  secreted  by  the  posterior  surface  of  the  iris  and  ciliary  body. 
It  passes  through  the  pupil  into  the  anterior  chamber. 

The  globe  of  the  eye  is  filled  with  fluids  during  life  and  is  con- 
stantly under  a  certain  pressure:  the  intra-ocular.  This  pressure 
depends  mainly  upon  the  arterial  pressure  of  the  retinal  arteries,  and 
so  rises  and  falls  with  their  variations  of  pressure. 

EETINAL  EPITHELIUM. — Fuscin,  a  variety  of  melanin,  is  found  in 
the  hexagonal  cells  of  the  retinal  epithelium.  The  cells  send  down 
processes  between  the  rods  and  cones  like  the  hairs  of  a  brush.  It  has 
been  found  that  light  exerts  a  marked  effect  upon  these  processes. 
The  protoplasm  of  the  pigment-cells  of  a  frog  that  has  been  kept  in 
the  dark  for  several  hours  is  found  to  be  retracted  and  the  pigment  lies 
chiefly  in  the  body  of  the  cell.  When  exposed  to  the  light  the  proc- 
esses filled  with  pigment  dip  down  between  the  rods  and  cones  as  far 
as  the  external  limiting  membrane. 

LYMPHATICS. — The  lymphatics  of  the  eye  comprise  an  anterior 
and  posterior  set.  The  former  is  located  in  the  anterior  and  posterior 
chambers  of  the  eye  and  have  communication  with  the  lymphatics  of 
the  iris,  ciliary  processes,  cornea,  and  conjunctiva.  The  posterior  set 
consists  of  the  perichoroidal  spaces  lying  between  the  choroid  and 
sclerotic  coats  of  the  eyeball. 

Optic  Nerve. 

The  optic  nerve-apparatus  comprises  (1)  the  optic  tracts,  (2) 
the  optic  commissure.,  and  (3)  the  optic  nerves. 

The  centripetal  fibers  of  the  optic  nerve  are  the  neuraxons  of 
the  ganglionic  cells  of  the  second  layer  of  the  retina.  The  dendrons 
of  these  cells  receive  arborizations  from  the  neuraxons  of  the  bipolar 
cells  of  the  retina.  The  dendrons  of  the  bipolar  cells  end  about  the 
neuraxons  of  the  visual  cells,  whose  dendrons  are  the  rods  and  cones. 


VISION.  517 

Hence  there  is  a  conducting  path  through  the  retina  continuous  with 
the  optic  nerve  which  decussates  in  part  and  connects  with  the  ex- 
ternal geniculate  body,  the  pulvinar  of  the  optic  thalamus,  and  the 
anterior  corpora  quadrigemina.  From  these  parts  new  neuraxons 
arise  which  issue  from  the  outer  side  of  the  thalamus,  and  run  through 
the  extreme  end  of  the  thalamus,  ending  chiefly  in  the  cuneus  and 
occipital  lobes.  These  are  the  optic  radiations  of  Gratiolet. 

The  union  of  the  two  tracts  produces  the  optic  commissure,  or 
optic  chiasma. 

It  is  in  the  commissure  that  there  occurs  a  partial  decussation  of 
the  fibers  of  the  two  tracts.  More  than  one-half  of  the  fibers  of  the 
one  tract  cross  over  to  those  of  the  opposite  tract.  That  is,  the  left 
tract  sends  fibers  to  the  left  half  of  both  eyes ;  the  right  tract  in  turn 
supplies  the  right  half  of  each  eye.  Destruction  of  the  optic  tract, 
then,  produces  homonymous  hemianopsia;  that  is,  the  outer  half  of 
one  eye  and  the  inner  half  of  the  other  is  blind.  In  owls  there  is 
complete  decussation,  so  that  destruction  of  one  tract  back  of  the 
decussation  produces  blindness  in  the  whole  eye  of  the  side  opposite  to 
the  lesion. 

From  the  optic  commissure  proceed  the  two  optic  nerves:  one 
to  each  eyeball.  Each  optic  nerve  is  inclosed  within  a  sheath  of  its 
own,  composed  of  dura  mater  and  arachnoid. 

Perception  of  Light. 

Light  is  due  to  vibrations  of  ether;  a  proper  conception  of  them 
gives  the  sensation  of  sight.  Transmission  of  light,  with  air  as  a 
medium,  is  186,000  miles  per  second.  The  rapidity  of  the  vibrations 
influences  the  sensation  produced,  for  color  is  for  luminous  sensation 
what  height  is  for  sound.  The  inferior  limit  of  visible  vibrations  is 
represented  by  the  color  red ;  the  superior  limit  is  exemplified  in  violet. 

For  light  to  be  perceived  physiologically  by  any  individual  it  must 
make  an  impression  upon  the  retina.  The  light  falling  upon  the 
retina  immediately  stirs  up  certain  changes  in  it  which  in  turn  give 
rise  to  nervous  changes  in  the  fibers  of  the  optic  nerve.  This  last 
change,  or  "visual  impulse/'  produces  a  further  series  of  events 
within  the  brain,  one  effect  of  which  is  a  change  in  our  consciousness ; 
that  is,  there  is  a  sensation. 

The  point  upon  the  retina  at  which  the  impressions  are  strongest 
and  most  exact  is  the  macula  lutea  and  its  fovea  centralis.  The 
anatomical  layer  designed  to  be  impinged  upon  by  a  distinct  image  is 
the  membrane  of  Jacobson,  the  layer  of  rods  and  cones.  As  only  the 


518  PHYSIOLOGY. 

cones,  and  no  rods,  are  found  in  the  fovea  centralis,  it  is  the  point 
where  objects  are  fixed.  Hence  it  must  be  held  that  the  cones  are  the 
specific  elements  of  the  retina  that  are  designed  to  make  the  indi- 
vidual perceive  a  luminous  impression  precisely.  Nevertheless,  the 
field  of  vision,  though  indistinct  toward  its  periphery,  is  very  much 
enlarged. 

The  luminous  impression  consists  of  the  vibrations  of  the  lumi- 
nous ether,  which  stimulate  the  outer  portion  of  the  rods  and  cones. 
In  them  there  is  produced  a  molecular,  mechanical  change,  or  dis- 
turbance. Whenever  the  layer  of  rods  and  cones  is  stimulated,  the 
excitation  is  propagated  from  without  inward  to  all  of  the  retinal  ele- 
ments. The  various  elements  are  connected  by  fibers,  and,  finally,  by 
the  optic  nerve  with  the  brain. 

Physiology  of  the  Eye. 

The  study  of  the  phenomena  of  the  eye  may  be  divided  into  four 
parts:  (1)  dioptrics.,  (2)  accommodation,  (3)  imperfections  and  cor- 
rections., and  (4)  vision  with  both  eyes. 

Dioptrics. — The  eye  has  previously  been  mentioned  as  being  like 
a  camera  obscura.  If  a  small  opening  exist  in  the  shutter  of  a  dark 
room  the  rays  of  light  from  the  outside  passing  through  the  opening 
will  form  an  inverted  image  of  the  external  object  upon  the  opposite 
wall  of  the  chamber.  However,  unless  the  opening  be  very  small,  the 
image  will  be  blurred  and  indistinct.  These  latter  qualities  will  be 
due  to  overlapping  of  rays  of  light  from  various  points  of  the  object. 
If  the  opening  be  small  enough  the  overlapping  rays  will  be  cut  off 
and  a  distinct  image  be  formed.  Should  a  convex  lens  be  interposed 
in  the  path  of  the  rays  of  light  the  opening  may  be  very  considerably 
enlarged  and  yet  the  various  rays  be  brought  to  a  focus  so  that  diffused 
images  will  be  prevented. 

The  camera  obscura  is  popularly  known  to-day  in  the  form  of 
the  photographic  camera.  The  latter  consists  of  a  box  blackened  on 
the  interior  to  prevent  reflection  from  the  walls.  In  front  is  a  short 
tube  which  contains  achromatic  lenses.  In  the  back  wall  of  the 
camera  is  found  a  ground-glass  plate  upon  which  the  image  formed 
by  the  lens  is  focused.  If  the  camera  be  so  adapted  that  parallel 
rays  falling  upon  the  lens  are  focused  upon  the  ground-glass  plate, 
then  divergent  rays  must  have  their  focal  point  behind  the  plate. 
Should  the  plate  be  moved  backward  or  forward  it  can  be  made  to 
coincide  with  the  conjugate  focus  of  the  rays  diverging  from  the 
object. 


VISION.  519 

SPHERICAL  ABERRATION,  which  interferes  with  distinctness,  is 
gotten  rid  of  by  cutting  off  outside  rays.  In  the  camera  this  point  is 
accomplished  by  the  insertion  of  a  diaphragm  through  a  slit  in  the 
lens-tube.  The  diaphragm  is  pierced  by  holes — a  larger  or  smaller  one 
being  used  according  as  the  light  is  feeble  or  strong. 

The  eye  may  be  very  aptly  compared  to  the  camera.  It  has  a 
small  opening  in  front  through  which  pass  the  rays  of  light.  The 
sclerotic  and  choroid  coats  form  its  walls.  The  refracting  lenses  are 
the  cornea,  aqueous  humor,  crystalline  lens,  and  vitreous  humor. 
They  all  tend  toward  the  accomplishment  of  the  same  end:  to  bring 
parallel  rays  of  light  to  a  focus  upon  a  sensitive  plate  (the  retina), 


Fig.   126. — Diagram  Illustrating  Spherical  Aberrations. 

The  rays  passing  through  the  edge  of  the  lens  have  a  shorter  focal  distance  than 
those  passing  nearer  to  the  center. 

there  to  form  a  real  inverted  image  of  the  object.  Last,  the  iris  with 
its  pupil  acts  as  a  diaphragm. 

CHROMATIC  ABERRATION. — The  edge  of  the  lens  of  a  camera  rep- 
resents the  outer  angle  of  a  prism.  White  light  falling  upon  it  is 
decomposed  into  its  spectral  components.  Objects  seen  upon  the 
ground-glass  plate  have  an  iridescent  hue.  In  the  eye  this  trouble  is 
obviated  by  the  presence  of  the  iris  and  the  fact  of  the  edge  of  the 
lens  being  more  angular  and  less  curved. 

VISUAL  ANGLE. — It  has  been  stated  by  Helmholtz  that  the  visual 
angle  is  really  the  angle  inclosed  by  visual  lines,  which  are  lines  from 
a  point  in  space  which  pass  through  the  center  of  the  image  of  the 
pupil  formed  by  the  cornea  and  pass  to  the  center  of  the  macula  lutea. 
The  apparent  size  of  the  object  depends  upon  the  visual  angle.  Acute- 
ness  of  vision  is  inverse  as  the  size  of  the  visual  angle.  The  test-types 


520 


PHYSIOLOGY. 


of  Snellen  are  constructed  on  this  principle.  They  are  adjusted  to 
be  seen  under  an  angle  of  five  minutes. 

Accommodation  of  Eye  for  Distance. — The  refractive  media  of 
the  eye  are  such  that  parallel  rays  are  brought  to  a  focus  upon  the 
retina.  Such  an  eye  is  said  to  be  emmetropic. 

It  is  evident  that,  if  divergent  rays  fall  upon  the  eye, — that  is, 
rays  from  a  finite  distance, — they  will  not  be  brought  to  a  focus  upon 
the  retina,  but  behind  it  if  the  eye  remain  in  its  emmetropic  condition. 
The  result  of  this  would  be  circles  of  diffusion  and  a  blurred  and 
indistinct  image. 


Fig.  127. — Scheme  of  Accommodation  for  Near  and  Distant  Objects. 
(LANDOIS,  after  Helmholtz.} 

The  right  side  of  the  figure  represents  the  condition  of  the  lens  during  accommoda- 
tion for  a  near  object  and  the  left  side  when  at  rest.  The  letters  indicate  the  same 
parts  on  both  sides  ;  those  on  the  right  side  are  marked  with  a  stroke  (or  minute 
mark.  A,  Left  half  of  lens.  £,  Eight  half  of  lens.  C,  Cornea.  S,  Sclerotic.  CS,  Canal 
of  Schlemm.  VIC,  Anterior  chamber.  J,  Iris.  P,  Margin  of  pupil.  V,  Anterior  sur- 
face. If,  Posterior  surface  of  lens,  ft,  Margin  of  the  lens.  F,  Margin  of  ciliary  proc- 
esses, a,  b,  Space  between  the  two  former.  The  line  Z~X  indicates  the  thickness  of 
the  lens  during  accommodation  for  a  near  object ;  Z-Y,  the  thickness  of  the  lens  when 
the  eye  is  passive. 

Should  the  refractive  power  of  the  media  be  increased,  then  the 
focal  point  would  be  brought  forward.  Such  increase  might  be  accom- 
plished by  the  addition  of  another  convex  lens  in  front  of  the  crystal- 
line  lens. 

The  effect  is  practically  accomplished  by  reason  of  the  lens  being 
able  to  adjust  its  capacity  to  suit  varying  distances.  This  capacity  is 
termed  the  power  of  accommodation.  It  is  an  ability  to  alter  the  con- 
vexity of  the  lens,  due  to  contraction  of  the  ciliary  muscles  which  relax 
the  zonule  of  Zinn  of  the  lens.  By  reason  of  its  own  elasticity  the  lens 
bulges  forward,  thus  increasing  its  convexity. 

In  what  may  be  regarded  as  the  normal,  or  so-called  emmetropic 
eye,  the  near  point  of  accommodation  is  about  five  inches.  The  far  f 


VISION.  521 

limit,  for  all  practical  purposes,  is  from  two  hundred  feet  up  to  an 
infinite  distance.  In  this  eye  the  range  of  distinct  vision  has  wide 
latitudes. 

In  the  myopic,  or  short-sighted,  eye  the  near  point  is  two  and 
one-half  inches  from  the  cornea.  The  far  limit  is  at  a  variable,  but 
not  very  great  distance.  The  range  of  vision  in  this  eye  is  very  lim- 
ited. In  this  the  rays  of  light  are  brought  to  a  focus  in  front  of  the 
retina. 


Fig.  128. — Myopic  Eye.     (LANDOIS.) 

In  the  hypermetropic^  or  far-sighted,  eye  rays  of  light  coming 
from  an  infinite  distance  are,  in  the  passive  state  of  the  eye,  brought 
to  a  focus  behind  the  retina.  The  near  point  is  some  distance  away. 

The  presbyopia,  or  long-sighted,  eye  of  aged  persons  resembles 
the  hypermetropic  eye,  but  differs  in  so  far  that  the  former  is  an 
essentially  defective  condition  of  the  mechanism  of  accommodation. 


Fig.  129. — Hypermetropic  Eye.     (LANDOIS.) 

There  are  two  changes  which  occur  when  we  accommodate  for 
near  objects :  one  is  that  the  pupil  contracts  to  cut  off  divergent  rays; 
the  other  is  a  change  of  curvature  of  the  lens.  The  ciliary  muscle  is 
the  motive  power  of  accommodation.  Its  paralysis  renders  accommo- 
dation impossible.  The  oculomotor  innervates  the  ciliary  muscle. 
Its  paralysis  by  atropine  produces  both  dilatation .  of  the  pupil  and 
inability  to  accommodate. 


522 


PHYSIOLOGY. 


To  correct  anomalies  of  refraction  it  is  necessary  to  use  lenses. 
These  are  transparent  media  which  seem  to  refract  rays  of  light 
passing  through  them.  They  have  curved  surfaces.  The  direction 
which  the  rays  take  on  emerging  from  the  medium  depends  upon  the 
nature  of  the  curvature.  The  chief  forms  of  lenses  are  convex  and 
concave;  convex  lenses  may  be  doubly  convex,  plano-convex,  or  con- 
cavo-convex. A  concave  lens  may  have  equivalent  features.  A  con- 
vex lens  converges  the  rays  of  light ;  a  concave  lens  diverges  the  rays 
of  light.  In  myopia  a  concave  lens  is  used;  in  hypermetropia  and 
presbyopia  a  convex  lens. 

Astigmatism  is  a  defect  of  refraction  due  to  a  want  of  symmetry 
in  the  refracting  media  of  the  eye.  The  result  of  this  is  that  the 
rays  of  light  passing  through  the  lens  are  not  brought  to  a  focus  at 
the  same  point.  This  want  of  symmetry  is  usually  in  the  cornea,  but 
may  be  in  the  lens.  To  remedy  this  defect  we  use  a  lens  called  a 


Fig.   130. — Different   Kinds   of   Lenses.     (GANOT.) 

A,  Double  con  vex.     B,  Plano-convex.      C,  Converging  concavo-convex.     D,  Double 
JF1,  Diverging  concavo-convex. 


concave.      E,  Plano-concave, 
meniscus  lenses. 


C  and  .Fare also  called 


cylinder  to  level  up  the  curvature  of  one  of  the  meridians  of  the 
cornea  to  correspond  to  the  curvature  of  the  others.  Cylinders  have 
no  curvature  in  one  axis,  but  more  or  less  considerable  curvature  in 
the  opposite  axis  in  correspondence  with  the  degree  of  astigmatism 
that  has  to  be  corrected. 

LENSES. — Lenses  are  arranged  according  to  their  focal  distance 
in  inches,  and,  as  the  unit  was  taken  as  one  inch,  all  weaker  lenses 
were  expressed  in  fractions  of  an  inch.  However,  Donders  made  the 
standard  in  lenses  of  a  focal  distance  of  one  meter,  and  this  unit  he 
called  a  dioptre.  Thus  the  standard  in  a  weak  lens  and  the  stronger 
lens  are  multiples  of  these.  Hence  a  lens  of  two  dioptres  equals  one 
of  about  twenty  inches'  focus. 

ENTOPTIC  PHENOMENA. — When  in  the  vitreous  there  exist  cel- 
lular elements  which  in  the  field  of  vision  appear  as  strings  of  beads, 
circles,  and  stripes,  they  are  called  muscae  volitantes.  They  move 
when  the  eye  is  moved.  If  the  eye  is  strongly  illuminated  at  the  side, 


VISION.  523 

branching  figures  are  seen  in  the  field  of  vision,  which  are  called 
Purkinje's  figures.  They  are  due  to  shadows  of  the  blood-vessels  of 
the  retina  which  fall  upon  the  rods  and  cones. 

DURATION"  OF  KETINAL  STIMULATION. — Light  impresses  the  ret- 
ina, but  the  excitation  of  it  does  not  cease  immediately  with  the 
disappearance  of  the  luminous  vibrations.  Indeed,  they  persist  for 
a  certain  time,  about  one-eighth  of  a  second :  that  is,  proportional  to 
the  intensity  of  the  excitation.  Upon  a  disc  black  and  white  sections 
are  alternately  painted.  When  the  disc  is  made  to  rotate  rapidly  the 
disc  appears  neither  black  nor  white,  but  gray. 

VISUAL  PURPLE,  OR  EHODOPSIN. — The  outer  part  of  the  rods  con- 
tains a  reddish  coloring  matter  which  is  called  visual  purple.  This 
coloring  matter  must  be  kept  in  the  dark,  for  it  bleaches  the  moment 
light  strikes  it.  But  the  color  will  return  if  the  eye  is  again  brought 


Fig.  131. — Diagram  Showing  Refraction  by  a  Double  Convex 
Lens.     (GANOT.) 

The  incident  ray,  Ij-S,  is  refracted  at  the  points  of  incidence,  B,  and  emergence, 
D,  toward  the  axis,  M-N-A,  which  it  cuts  at  F. 

into  a  dark  chamber.  The  bile  acids  extract  the  coloring  matter  from 
the  retina.  The  visual  purple  is  a  product  of  the  melanin  or  fuscin. 
Color-vision. — White  light  is  composed  of  rays  of  different  re- 
frangibility  by  reason  of  the  different  length  and  duration  of  the 
luminous  rays*  These  various  rays  falling  upon  the  retina  determines 
in  the  individual  different  sensations  which  correspond  to  the  colors. 
To  decompose  white  light  into  its  different  colors,  the  prism  is  used. 
A  ray  of  white  light  upon  issuing  from  the  prism  presents  the  spec- 
trum. That  is,  there  emerge  the  principal  simple  colors  from  the 
most  to  the  least  refrangible.  They  are  violet,  indigo,  blue,  green, 
yellow,  orange,  and  red.  Each  primary  color  cannot  be  further  de- 
composed, but  all  can  be  reunited  by  a  biconvex  lens  so  that  white 
light  will  result  again.  The  ultra-red  (thermal)  and  ultraviolet 
(chemical)  rays  do  not  make  any  impression  upon  the  retina.  The 
former  do  not  pass  through  the  media  of  the  eye,  since  to  vibration- 
rates  beneath  435,000,000,000  per  second  the  retina  is  not  stimu- 


524  PHYSIOLOGY. 

lated;  the  latter  color  produces  no  sensation,  since  to  vibration-rates 
above  764,000,000,000  per  second  the  retina  is  insensible. 

SENSATIONS  OF  COLOR. — In  the  production  of  the  sensations  of 
color  there  are  three  chief  factors :  tone,  saturation,  and  intensity. 
The  tone  of  the  color  depends  upon  the  number  of  vibrations  of  the 
ether.  A  color  is  said  to  be  saturated  when  it  does  not  contain  any 
white  light.  The  simple  colors  of  the  spectrum  are  saturated.  The 
intensity  of  color  depends  upon  the  amplitude  of  the  vibrations. 

Loss  or  COLOR-VISION,  OR  DALTONISM. — Young  stated,  as  the  ex- 
planation of  color-vision,  that  all  the  colors  were  referable  to  three 
fundamental  sensations:  those  of  red,  green,  and  violet.  Corre- 


Fig.  132. — Diagram  Illustrating  the  Decomposition  of  White  Light  into 
the   Seven  Colors   of  the   Spectrum  in  Passing 

Through  a  Prism.     (BECLARD.) 
r,  Red.     o,  Orange,    j,  Yellow,     v,  Green.     6,  Blue,     i,  Indigo,     vi,  Violet. 

spending  to  the  three  sensations  excited  by  these  three  colors  were 
three  kinds  of  retinal  fibers,  stimulation  of  which  gives  rise  to  sen- 
sations of  red,  green,  and  violet.  It  is  also  supposed  that  white  light 
stimulates  these  fibers  with  different  degrees  of  activity  according  to 
the  length  of  the  wave.  The  longest  wave  acts  most  on  the  fibers 
which  respond  to  the  red  color,  the  medium  wave  on  the  fibers  which 
respond  to  green,  and  the  shortest  wave  on  the  violet.  Helmholtz 
adopted  the  theory  of  Young.  It  is  also  supported  by  the  facts  of 
color-blindness,  in  which  there  is  an  inability  to  distinguish  one  or 
more  of  the  fundamental  colors.  The  commonest  form  of  color- 
blindness is  that  in  which  red  is  the  invisible  color,  and  in  the  com- 


VISION.  525 

pound  colors  in  which  red  enters  the  complementary  color  alone  is 
visible,  white  appearing  as  bluish  green.  Another  theory  of  color- 
vision  is  that  of  Hering.  The  six  sensations  of  color  readily  fall  into 
three  pairs,  the  members  of  each  pair  having  similar  relationship. 
White  and  black  naturally  go  together,  the  one  being  antagonistic 
of  the  other.  According  to  Hering,  the  retina  is  undergoing  meta- 
bolic changes,  and  he  supposes  there  are  three  distinct  visual  sub- 
stances which  are  undergoing  anabolism  and  catabolism.  When 
breaking  down,  or  catabolism,  is  in  excess  of  the  building  up,  or 
anabolism,  we  have  a  sensation  of  white;  when  upbuilding  predomi- 
nates, we  have  black. 

Anabolism  of  the  visual  substances  by  the  rays  of  light  produces 
green,  blue,  and  black;  catabolism  of  these  visual  substances  pro- 
duces white,  red,  and  yellow. 

{White  is  catabolic  C    Red  is  catabolic 

and  2.    J         and 

Black  is  anabolic.  (^    Green  is  anabolic. 

f   Yellow   is   catabolic 
3.  J         and 

I     Blue  is  anabolic. 

In  applying  this  theory  to  color-blindness  it  must  be  assumed 
that  those  who  are  red-blind  want  the  red-green  visual  substance; 
they  have  only  the  black-white  and  yellow-blue  visual  substance  in 
the  retina. 

According  to  the  Young-Helmholtz  theory,  there  is  a  defect  cor- 
responding to  the  three  color-perceiving  fibers.  According  to  this 
theory  color-blindness  is  of  four  kinds:  red,  green,  and  violet,  and 
complete  blindness  to  colors.  In  the  Hering  theory  the  kinds  are: 
(1)  complete,  (2)  blue-yellow,  (3)  red-green,  and  (4)  incomplete  color- 
blindness. 

Color-blindness  is  also  called  Daltonism,  after  Dalton,  a  Quaker, 
who  first  described  it.  The  percentage  of  color-blindness  among 
persons  is  about  3,  and  among  Quakers  about  3  1/2,  because  for  gen- 
erations they  have  worn  drabs.  The  disease  is  hereditary. 

COMPLEMENTARY  COLORS.  -  -  Those  colors  are  complementary 
which  when  mixed  together  produce  white.  The  following  table  gives 
the  complementary  colors  of  the  spectrum  :— 

Red — greenish  blue.  Greenish  yellow — violet. 

Orange — Prussian  blue.  Green — purple. 

Yellow — indigo-blue. 


526  PHYSIOLOGY. 

Green  alone  has  no  complementary  color  in  the  spectrum.  It 
gives  a  white  color  with  the  compound  color  purple. 

Irradiation. — This  is  a  phenomenon  which  is  observed  when  look- 
ing at  a  strongly  illuminated  object  upon  a  dark  background;  the 
.object  appears  larger  than  it  really  is.  Thus,  of  two  rings  of  equal 
size,  one  white  on  black,  the  other  black  on  white,  the  former  appears 
larger  than  the  latter.  Irradiation  is  due  to  imperfect  accommoda- 
tion. Here  the  margins  of  an  object  are  projected  upon  the  retina 
in  circles  of  diffusion  and  the  brain  tends  to  increase  the  ill-defined 
margin  to  those  parts  of  the  visual  image  which  are  most  prominent 
in  the  image  itself.  What  is  bright  seems  larger  and  overcomes  what 
is  dark.  Black  clothes  make  one  appear  to  be  much  smaller  than 
light  clothes. 

After-images. — When  a  bright  light  is  thrown  on  the  eye  and 
then  suddenly  put  out,  there  remains  for  a  short  time  an  impression 


Fig.   133. — Diagram  Illustrating  Irradiation.      (STIRLING.) 

If  this  diagram  is  held  some  distance  from  the  eye  especially  if  not  exactly  focused, 
the  white  dot  will  appear  larger  than  the  black,  though  both  are  of  exactly  the  same 
size. 

of  the  same  light,  as  though  the  retinal  molecules  still  continued  to 
vibrate  from  the  light  stimulus.  This  is  a  positive  after-image. 
When  the  eye  has  received  a  stimulus  for  some  time,  the  sensation 
which  follows  the  withdrawal  is  of  a  different  kind,  and  you  have  a 
negative  after-image,  which  is  due  to  exhaustion  of  the  retinal  cells. 
For  instance,  if  you  look  at  a  red  color  for  some  time  and  the  eye 
afterward  is  focused  on  a  white  ground,  the  negative  after-image  is  a 
greenish-blue;  that  is,  the  color  of  the  negative  image  is  comple- 
mentary to  that  of  the  object. 

Phosphenes. — If  the  retina  be  pricked,  compressed,  or  twitched 
by  any  sudden  movement,  an  impression  of  light  will  be  produced. 
The  same  effect  follows  the  use  of  electricity.  Hence  the  retina 
is  an  essentially  sensitive  membrane.  No  matter  by  what  cause 
its  sensibility  be  excited,  it  always  gives  rise  to  the  subjective  phe- 
nomenon of  a  luminous  sensation. 


VISION.  527 

Vision  with  Both  Eyes. — The  study  of  phenomena  bearing  upon 
this  subject  comprises :  (1)  movements  of  the  eyes,  (2)  binocular  vision, 
and  (3)  the  advantages  of  sight  with  both  eyes. 

MOVEMENTS  OF  THE  EYES. — The  eyeball  may  be  considered  as  an 
articulated  spherical  globe  which  turns  upon  three  axes  that  cross 
each  other.  Six  voluntary  muscles  affect  the  three  rotations  of  the 
eye.  The  rectus  internus  and  externus,  when  acting  alone,  turn  the 
eye  from  side  to  side.  The  superior  and  inferior  recti  give  to  the 
ocular  sphere  an  up-and-down  movement.  The  superior  or  inferior 
oblique  muscle,  acting  alone,  gives  the  eye  an  oblique  movement. 

Co-ordinated  Movements. — The  two  eyes  always  present  co-ordi- 
nated movements  in  order  to  maintain  the  parallelism  or  convergence 
of  the  two  visual  lines.  The  visual  line  is  that  line  which  passes  be- 
tween the  object,  center  of  the  pupil,  and  center  of  rotation  of  the 
ocular  globe.  For  accommodation  at  a  distance  the  two  visual  lines 
are  parallel.  In  accommodation  for  near  objects  the  lines  are  con- 
vergent. 

So  long  as  the  muscles  of  the  eyeball  are  normal  in  function  their 
movements  are  in  co-ordination.  Should  one  or  more  become  para- 
lyzed or  seized  with  spasm,  then  proper  parallelism  and  convergence 
are  lost.  Strabismus  will  then  be  present  and  the  object  looked  at 
will  appear  double :  diplopia. 

The  innervation  of  the  muscles  of  the  eye  is  derived  from  the 
third,  fourth,  and  sixth  pairs  of  cranial  nerves. 

BINOCULAR  VISION. — Looking  into  space  with  one  eye,  one  sees 
an  almost  circular  field.  With  the  one  eye  he  can  look  toward  the 
opposite  side  as  far  as  the  root  of  the  nose  permits.  If  he  opens  the 
other  eye  the  visual  space  becomes  much  more  extended  in  a  trans- 
verse direction,  but  corresponding  to  the  monocular  field,  since  the  two 
monocular  fields  are  superposed. 

Why  should  any  point  or  object  be  seen  single  and  not  double, 
when  the  point  forms  not  one,  but  two  images  upon  the  retinae? 
The  explanation  accepted  is  that  the  images  are  as  two  corresponding 
identical  points.  These  points  are  so  related  to  one  another  that  the 
sensations  from  each  are  blended  into  one  perception.  The  move- 
ments of  the  eyeballs  are  also  adapted  to  bring  the  image  of  the 
object  to  fall  upon  identical  parts.  The  law  results  that  if  one 
luminous  point  simultaneously  impresses  two  identical  points,  it  must 
be  seen  as  single  and  not  double.  The  two  images  are  referred  to 
one  point  in  space  and  they  produce  in  the  individual  only  one. im- 
pression. 


528 


PHYSIOLOGY. 


Lacrymal  Secretion. — Lately  it  has  been  shown  by  Landolt  that 
in  the  rabbit  and  the  monkey  secretory  nerves  of  the  lacrymal  gland 
run  in  the  facial  nerve.  These  nerves  leave  the  geniculate  ganglion 
and  enter  the  superficial  petrosal.  We  then  find  them  in  the  supe- 
rior maxillary  and  occasionally  in  the  ophthalmic.  He  believes  these 
fibers  run  in  the  glosso-pharyngeal  and  then  in  the  facial,  but  he  did 
not  locate  the  nucleus  from  which  they  arise. 

Ophthalmoscope. — This  is  a  small  concave  mirror  by  means  of 
which  rays  of  light  are  directed  through  the  pupil  of  the  eye  so  that 


Fig.  134. — Diagram  Illustrating  Binocular  Vision.     (BECLARD.) 

The  lines  from  the  object  indicate  that  rays  from  the  back  of  the  book  fall  on 
coincident  points  of  the  retina,  while  each  eye  further  has  a  special  field  of  vision. 

the  deep  parts  are  illuminated  and  made  visible.  There  is  a  hole 
in  the  center  of  the  mirror  through  which  the  examiner  looks.  But 
the  ophthalmoscope  may  be  used  with  or  without  lenses.  Without 
lenses  the  ophthalmoscope  gives  an  erect  image.  If,  however,  we 
use  a  convex  lens  over  the  central  aperture  of  the  ophthalmoscopic 
mirror  the  observer  sees  a  reinverted  image.  If  a  concave  lens  is 
used  over  the  aperture  of  the  ophthalmoscopic  mirror  there  is  seen 
an  erect  image  considerably  magnified.  The  instrument  is  usually 
fitted  with  a  series  of  concave  and  convex  mirrors,  which  can  be  re- 
volved in  front  of  the  central  aperture  of  the  mirror. 


VISION.  529 

If  the  observer  is  myopic  he  can  use  the  concave  lenses  to  correct 
his  myopia.  If  he  is  long-sighted,  he  corrects  it  by  means  of  one  of 
the  convex  lenses. 

If  the  eye  examined  be  short-  or  long-  sighted,  the  retinal  image 
could  not  be  brought  into  focus  with  the  mirror  alone,  but  the  ex- 
aminer can  adjust  his  concave  or  convex  disc,  as  the  case  may  be,  and 
find  a  lens  to  correct  the  short  or  long  sight  of  the  eye  examined. 

In  this  way  the  ophthalmoscope  may  be  used  to  measure  the 
degree  of  myopia  or  hypermetropia  of  the  eye  examined. 

Perimeter. — It  has  been  noted  that  by  the  peripheral  parts  of  the 
retina  a  person  can  observe  pretty  definitely  the  form  and  color  of 
objects.  To  determine  just  how  far  this  field  of  indirect  vision  ex- 
tends in  every  direction  from  the  visual  axis  is  to  locate,  by  the 
perimeter,  the  field  of  indirect  vision.  The  instrument  devised  for 
this  purpose  is  called  the  perimeter. 

With  the  perimeter  the  eye  is  made  to  view  a  fixed  point  from 
which  a  quadrant  proceeds  so  that  the  eye  lies  in  the  center  of  it. 
Around  the  fixed  point  the  quadrant  rotates,  and  this  circumscribes 
the  surface  of  a  hemisphere  in  the  center  of  which  the  eye  is  located. 
From  this  fixed  point  objects  are  slid  on  semicircular  arms  and  are 
gradually  placed  more  toward  the  periphery  of  the  field  of  vision 
until  the  object  is  no  longer  noticed.  Then  by  moving  the  semi- 
circular arm  in  different  meridians  of  the  field  of  vision  we  obtain 
what  is  called  the  field  of  vision.  The  field  of  vision  is  more  extended 
below  and  to  the  outer  side.  It  is  narrowed  above  by  the  brow; 
below  by  the  cheek  and  the  nose. 


CHAPTER  XX. 

CRANIAL    NERVES. 

THE  cranial  nerves  are  twelve  pairs  of  nerves  which  reach  their 
respective  terminations  after  passage  through  foramina  located  in  the 
base  of  the  cranium.  They  are  designated  numerically,  beginning  from 
the  anterior  portion  of  the  base  of  the  brain  backward,  as  well  as  by 
names  dependent  upon  their  functions  and  distribution.  They  are  as 
follows : — 

1.  Olfactory.  5.  Trifacial.  9.  Glosso-pharyngeal. 

2.  Optic.  6.  Abducent.  10.  Pneumogastric. 

3.  Motor  oculi.  7.  Facial.  11.  Spinal  accessory. 

4.  Pathetic.  8.  Auditory.  12.  Hypoglossal. 

Origin  of  the  Cranial  Nerves, — Upon  examination,  each  cranial 
nerve  is  found  to  possess  a  point  of  superficial  origin  as  well  as  a 
nucleus  of  deep  origin. 

The  superficial  origin  is  that  point  upon  the  brain's  surface  where 
each  nerve  emerges.  This  is  but  the  apparent  origin  of  each  pair  of 
nerves,  since  their  individual  fibers  may  be  traced  more  deeply. 

Each  cranial  nerve  has  a  special  nucleus  of  gray  matter  lying 
deeply  within  the  brain-substance.  The  nucleus  consists  of  a  collec- 
tion of  cells  from  whose  prolongations  spring  the  axis-cylinders  which 
constitute  the  fibers  of  the  nerves. 

The  gray  masses  which  represent  the  prolongations  of  the  anterior 
horns  of  the  cord  into  the  medulla  oblongata  form  the  nuclei  of  origin 
of  the  cranial  motor  nerves.  The  base,  separated  from  the  head  of  the 
horn  by  decussation  of  the  pyramidal  columns,  remains  contiguous 
to  the  central  canal.  It  is  prolonged  in  its  entirety  upon  the  floor 
of  the  fourth  ventricle,  lying  upon  each  side  of  the  raphe.  Beneath 
the  trigonum  hypoglossi  lies  the  nucleus  of  the  hypoglossal ;  beneath 
the  eminentia  teres  is  found  the  common  nucleus  of  the  facial  and 
motor  oculi;  the  nuclei  of  the  abducent  and  pathetic  lie  upon  each 
side  of  the  aqueduct. 

The  head  of  the  anterior  horn,  cut  into  fragments  by  the  motor 

decussation,  forms  that  which  is  known  as  the  antero-lateral  nucleus. 

This  is  the  motor  nucleus  of  the  mixed  nerves.    By  its  most  internal 

parts  it  represents  the  accessory  or  anterior  nucleus  of  the  hypo- 

(530) 


CRANIAL  NERVES.  531 

glossus;  farther  up,  the  proper  nucleus  of  the  facial;  and  in  the 
pons  there  is  found  the  motor  root  of  the  trigeminus. 

The  gray  masses  of  the  posterior  horns  of  the  cord,  prolonged 
into  the  medulla  oblongata  and  cut  by  the  sensory  decussation  or  fillet, 
form  the  sensitive  nuclei  of  the  cranial  nerves.  The  base  of  the  poste- 
rior horn  forms  the  sensory  nucleus  of  the  mixed  nerves,  namely: 
glosso-pharyngeal,  vagus,  and  spinal  accessory.  Above  these  nuclei 
there  is  a  gray  layer  which  represents  the  oblongata  center  of  the 
internal  root  of  the  auditory;  higher  still  arises  the  sensory  nucleus 
of  the  trigeminus.  The  head  of  this  horn,  under  the  name  of  gray 
nucleus  of  Rolando,  ascends  in  the  pons  to  form  the  ascending  root 
of  the  trigeminus. 

Among  the  twelve  pairs  of  cranial  nerves,  ten  have  their  points 
of  origin  in  cells  of  the  gray  matter  of  the  cord.  This  latter  has  been 
prolonged  into  the  medulla  oblongata  and  pons  in  the  form  of  four 
motor  and  sensory  columns.  Thus  these  cranial  nerves  are  com- 
parable to  spinal  nerves. 

Comparison  with  Spinal  Nerves. — The  law  of  double  root  is  as 
applicable  here  as  to  the  spinal  nerves.  Those  nerves  destined  for 
movement  originate  in  the  prolongations  of  the  anterior  horns,  while 
those  which  preside  over  sensibility  take  their  origin  in  gray  matter 
of  the  medulla  and  pons  which  has  sprung  from  the  posterior  horns 
of  the  spinal  cord. 

POINT  OF  DIFFERENCE. — There  is  this  difference,  however,  be- 
tween cranial  and  spinal  nerves :  In  the  spinal  nerves  the  two  roots  are 
intimately  united  just  outside  of  the  spinal-cord  substance  to  form 
a  mixed  nerve.  In  the  case  of  the  cranial  nerves  the  posterior  sensory 
roots  and  the  anterior  motor  roots  remain,  for  the  most  part,  sepa- 
rated to  form  nerves  that  are  either  exclusively  motor  or  exclusively 
sensory.  In  other  words,  the  cranial  nerves  represent  the  dissociated 
spinal  nerves  in  which  the  anterior  and  posterior  roots  remain  habit- 
ually isolated  to  form  nerves  which  are  either  fine  conductors  of 
motion  or  sensation,  dependent  upon  their  source. 

In  the  hypoglossal  alone  are  fulfilled  the  true  characteristics,  for 
in  numerous  cases  it  is  found  to  have  a  ganglion  upon  its  posterior 
root. 

The  mesencephalon  has  been  considered  to  possess  parallel  fea- 
tures with  the  spinal  cord,  in  that  it  is  formed  of  a  series  of  segments 
corresponding  to  the  cranial  nerves.  As  the  student  already  knows, 
each  spinal  nucleus  has  peripheral  conductors  which  bring  to  the  cord 
its  sensory  impressions,  and  motor  nerves  to  conduct  to  the  muscles 


532  PHYSIOLOGY. 

the  motor  reactions.  In  the  same  way  the  central  conductors  of  the 
brain  bring  to  it  sensory  impressions  and  by  its  motor  fibers  carry 
out  motion.  Hence  it  results  that  all  of  the  sensory  fibers  of  cen- 
tripetal course  have  their  origin,  not  in  the  gray  nuclei  of  the  medulla 
oblongata,  but  in  the  ganglia  annexed  to  the  dorsal  roots  of  the 
cranial  nerves. 

The  oblongata  nuclei  are  but  terminal  nuclei,  for  in  them  the 
sensory  fibers  terminate  by  fine  arborizations  which  surround  the 
central  cells  without  penetrating  them.  The  termination  is  identical 
with  that  of  the  sensory  roots  of  the  spinal  nerve. 

The  sensory  fibers  of  the  tenth,  ninth,  seventh,  and  fifth  pairs  of 
cranial  nerves,  as  well  as  that  of  the  auditory,  originate  in  their  re- 
spective ganglia.  Thus,  there  is  the  jugular  for  the  tenth  pair,  the 
petrosal  for  the  ninth  pair,  the  geniculate  for  the  seventh,  Gasserian 
for  the  fifth,  and  vestibular  ganglion  for  the  eighth  pair. 

On  the  contrary,  the  motor  fibers  of  the  cranial  nerves  arise  in 
the  central  cells  of  the  medulla  and  pons,  just  like  the  motor  fibers 
of  the  spinal  cord.  Thus,  fine  anatomy  demonstrates  that  the  cranial, 
like  the  spinal,  nerves  have  double  roots. 

Decussations.— The  afferent  or  sensory  cranial  nerves  do  not 
decussate.  Of  the  motor  cranial  nerves,  the  third  and  fourth,  the 
motor  root  of  the  fifth,  the  seventh,  the  motor  root  of  the  vagus, 
the  glosso-pharyngeal,  and  the  hypoglossal  decussate  partially.  The 
pathetic  decussates  completely  in  the  valve  of  Yieussens.  The  last- 
named  nerve  springs  from  the  oculomotor  nucleus  united  with  that 
of  the  pathetic.  These  portions  of  gray  matter  are  a  direct  part  of 
the  anterior  horn  of  the  spinal  cord  lying  beneath  the  aqueduct  of 
Sylvius. 

In  Chapters  XVII  and  XIX  were  considered  the  olfactory,  or  first 
pair  of  cranial  nerves,  and  the  optic,  or  second  pair;  so  that  in  this 
chapter  there  will  be  taken  up,  first,  the  motor  oculi,  or  third  pair 
of  cranial  nerves. 

THIRD  PAIR,  OR  MOTOR  OCULI  NERVE. 

This  nerve  arises  from  a  nucleus  situated  between  the  corpora 
quadrigemina  and  beneath  the  floor  of  the  aqueduct  of  Sylvius. 
Beneath  its  posterior  end,  the  corpus  quadrigeminum,  it  becomes 
continuous  with  the  nucleus  of  the  trochlearis  or  patheticus.  The 
oeulo-motor  nuclei  consist  (1)  of  a  group  of  cells  concerned  in  ac- 
commodation; (2)  those  concerned  in  the  reflex  action  of  the  iris  to 
light;  (3)  the  innervation  of  all  the  muscles  of  the  eye  except  the 


CRANIAL  NERVES. 


533 


external  rectus  and  superior  oblique.  The  neuraxons  of  these  cells 
pass  by  and  through  the  red  nucleus  and  emerge  at  the  inner  side  of  the 
cerebral  crura,  to  pass  through  the  interpeduncular  space  along  the 
outer  boundary  of  the  cavernous  sinus,  enter  the  sphenoidal  fissure, 
and  go  to  the  muscles  of  the  eyeball,  except  the  external  rectus  and 
superior  oblique.  It  also  gives  fibers  to  the  ciliary  muscle  and  the 
sphincter  of  the  pupil  and  a  branch  to  the  elevators  of  the  upper  lid. 
The  posterior  longitudinal  bundle  is  also  connected  with  the 
nuclei  of  the  third,  fourth,  and  sixth  nerves.  The  oculomotor  nucleus 
also  has  a  connection  with  the  optic  neurons  in  the  anterior  corpora 
quadrigemina.  In  the  cavernous  sinus  it  receives  filaments  coming 


I  ^rf./M/AwttB5.;^jJ.«-'v/vi*«i 

w   w  ^    .;  rF?--^~4::^5?&^     V 


"Ka.d  •  anter  tores 


,£K    IS.  ~EL- 

Fig.  135.— Position  of  the  Nuclei  of  the  Cranial  Nerves.     (After  EDINGEB.) 

The  medulla  oblongata  and  pons  are  imagined  as  transparent.   The  nuclei  of  origin 
(motor),  black  ;  the  end  nuclei  (sensory),  red. 

from  the  carotid  branches  of  the  great  sympathetic  nerve  and  also  a 
branch  from  the  ophthalmic  of  the  trigeminus. 

Functions. — From  a  functional  point  of  view,  it  may  be  said  that 
the  motor  oculi  is  devoted  exclusively,  in  conjunction  with  the  fourth 
and  sixth  pairs  of  nerves,  to  making  the  sight  perfect.  With  these 
nerves  it  concurs  to  regulate  the  varied  movements  which  allow  the 
eye  to  act  as  a  telescope  upon  a  support  that  is  furnished  with  numer- 
ous articulations.  By  means  of  these  muscles  and  nerves  of  the  orbit 
the  individual  is  enabled  to  remove  the  visual  field  from  place  to  place 
and  in  all  directions  to  any  objects  which  he  might  wish  to  examine. 

For  its  part,  the  motor  oculi  allows  the  eye  to  see  particularly 
objects  that  are  situated  high  or  low  or  at  one  side.  However,  it  has 
a  most  important  function  in  the  harmony  of  the  associated  move- 


534  PHYSIOLOGY. 

merits  by  which  two  images  fall  upon  identical  points  of  the  retinae 
of  the  two  eyes,  thus  causing  but  one  and  the  same  impression. 

The  third  pair  of  nerves  manages  to  regulate  the  amount  of  light 
which  falls  upon  the  retinae.  Its  function  in  this  capacity  is  to  pro- 
tect the  optic  nerve  against  a  too  intense  excitement  from  excessive 
light.  By  contracting  the  pupil  it  lessens  the  pencil  of  light  which 
penetrates  into  the  depths  of  the  ocular  globe. 

On  the  contrary,  it  is  the  sympathetic  which  produces  dilatation 
of  the  pupil  so  that  the  retina  may  receive  all  of  the  light  which  can 
be  reflected  from  obscure  objects.  For  the  accomplishment  of  con- 
traction and  dilatation  of  the  pupil  the  iris  comprises  two  kinds  of 
muscular  fibers:  circular  and  radiating.  The  former  are  connected 
with  the  motor  oculi;  the  latter  with  the  sympathetic. 

Finally,  the  third  nerve  is  considered  to  have  an  important  func- 
tion in  the  act  of  accommodation. 

Pathology. — The  motor  oculi  is  frequently  a  sufferer  by  reason 
of  its  situation  and  course.  It  is  often  compressed  by  tumors  at  the 
base  of  the  brain.  In  its  passage  through  the  sinus  cavernosus  it  is 
exposed  to  compression  by  a  thrombosis  of  this  venous  canal. 

The  course  of  the  third  nerve  through  the  interpeduncular  space 
makes  it  play  a  considerable  part  in  pathology.  This  is  the  place  of 
predilection  for  meningitic  deposits.  This  segment  of  the  nerve  is 
most  frequently  compressed  in  the  exudates  of  tubercular  meningitis. 
It  is  also  the  point  of  attack  of  constitutional  syphilis,  particularly 
during  the  tertiary  period;  this  is  a  chronic  meningitis  which  has  its 
principal  focus  at  the  interpeduncular  space  as  an  exudate.  Diph- 
theritic infection  often  attacks  the  third  pair  of  cranial  nerves. 

Paralysis  of  the  oculomotor  gives  rise  to  external  squint.  Its 
irritation  causes  internal  squint,  and  also  contraction  of  the  pupil, 
or  myosis.  The  eye  deviates  outward,  due  to  the  action  of  the  ex- 
ternal rectus  not  being  antagonized  by  the  internal  rectus. 

Diplopia. — The  deviation  of  one  of  the  eyes  does  not  permit  the 
maintenance  of  parallelism  of  the  visual  axes.  Without  this  coinci- 
dence the  two  images  will  not  fall  upon  identical  points  in  the  retina. 
Hence  all  objects  seen  will  be  double.  This  symptom,  known  as 
diplopia,  renders  the  sight  very  uncertain  and  often  produces  vertigo. 

Should  the  paralysis  be  general,  so  that  it  comprises  the  elevator 
of  the  lid,  Nature  brings  for  itself  a  remedy  for  the  defect  of  diplopia 
by  suppressing  the  vision  of  one  eye.  It  does  this  by  letting  the  lid 
fall  over  the  deviating  eye.  This  drooping  of  the  lid  gives  the  con- 
dition known  as  ptosis. 


CRANIAL  NERVES.  535 

Stimulation  of  the  motor  fibers  of  the  third  can  be  produced  re- 
flexly  by  teething  or  intestinal  irritations  of  children;  hence  their 
squint.  Chronic  spasms  of  the  eye-inuscles  which  are  involuntary  are 
called  by  the  name  nystagmus. 

Drugs. — Atropine  paralyzes  the  intra-ocular  ends  of  the  motor 
oculi;  Calabar  ~bean  stimulates  them  and  paralyzes  the  sympathetic. 

FOURTH  PAIR,  OR  PATHETIC  NERVE. 

Distribution. — The  pathetic  supplies  the  superior  oblique  muscle. 

Physiology. — If  the  peripheral  end  of  the  pathetic  be  electrically 
irritated,  the  superior  oblique  muscle  contracts  and  turns  the  eyeball 
downward  and  outward. 

The  pathetic  is  a  nerve  that  is  especially  endowed  for  the  realiza- 
tion of  simple  vision  with  the  two  eyes  in  inclined  positions  of  the 
head.  It  is  impossible  for  an  individual  to  carry  one  eye  downward 
and  outward.  That  is,  he  cannot  make  a  movement  directed  by  the 
superior  oblique  and  still  keep  the  head  perfectly  vertical.  It  be- 
comes necessary  that  the  head  be  inclined  to  one  side,  and  at  the 
time  this  inclination  is  produced  the  rotation  of  the  eyeball  occurs 
without  the  will  having  the  power  to  prevent  it.  By  the  very  act  of 
inclination  of  the  head  the  necessary  parallelism  of  the  two  eyes  is 
positively  destroyed;  hence  this  involuntary  action  of  the  superior 
oblique  to  place  the  visual  axes  upon  the  same  plane. 

The  fourth  pair  of  cranial  nerves  arise  from  a  collection  of  cells 
beneath  the  anterior  part  of  the  posterior  corpus  quadrigeminum.  It 
completely  decussates  in  the  superior  medullary  velum.  It  starts 
behind  the  quadrigeminal  body  and  then  appears  like  a  white  thread 
winding  around  the  outer  side  of  the  eras  of  the  cerebrum.  It  then 
pierces  the  dura  mater,  runs  along  the  outer  wall  of  the  cavernous 
sinus,  and  enters  the  sphenoidal  foramen  with  the  oculomotor  and 
abducent.  It  supplies  the  superior  oblique  muscle  of  the  eye. 

Pathology. — Usually  the  first  sign  of  any  disorder  of  the  pathetic 
is  a  giddiness  when  ascending  or  descending  a  stairs,  owing  to  the 
double  vision  that  occurs  when  the  patient,  in  going  down,  looks  at 
his  steps. 

To  overcome  this  diplopia  he  gives  to  his  head  a  position  that  is 
quite  characteristic.  He  holds  his  head  bent  forward  and  directed 
to  the  ground.  This  position  overcomes  the  necessity  of  moving  the 
eyeballs  from  above  downward  and  so  minimizes  the  liability  to 
diplopia. 


536  PHYSIOLOGY. 

SIXTH  PAIR,  OR  ABDUCENT  NERVE. 

This  nerve  arises  from  a  collection  of  cells  seated  beneath  the 
floor  of  the  fourth  ventricle  below  the  striae  acusticse.  The  loop  of 
the  facial  incloses  it.  The  abducent  emerges  between  the  summits 
of  the  pyramidal  bodies  of  the  medulla  oblongata  and  the  pons.  As 
a  threadlike  nerve  it  goes  through  the  cavernous  sinus  and  through 
the  sphenoidal  foramen  to  the  external  rectus.  The  nucleus  of  the 
abducent  has  a  connection  with  the  posterior  longitudinal  bundle  of 
fibers  to  the  opposite  oculomotor  nucleus,  thus  permitting  associated 
movements  of  the  eyeball.  The  pontal  olives  are  connected  by  fibers 
with  the  oculomotor  nucleus.  These  olives  are  also  connected  with 
the  auditory  nuclei,  and  these  nuclei  are  connected  with  the  cere- 
bellum; so  that  there  is  an  association  between  the  motor  nerves  of 
the  eye,  the  auditory  nerves,  and  the  cerebellum. 

Physiology. — The  sixth  nerve  is  exclusively  motor.  It  has  for 
its  only  aim  to  excite  the  external  rectus.  When  the  nerve  is  strongly 
galvanized  the  eyeball  deviates  outward.  Its  section,  on  the  contrary, 
produces  an  internal  strabismus.  It  is  especially  adapted  for  seeing 
objects  placed  to  one  side.  In  general,  the  abducent  is  but  one  of  the 
elements  for  the  exercise  of  perfect  vision. 

Pathology. — Paralysis  is  the  most  common  manifestation  in  the 
sixth  pair.  A  considerable  concussion  of  the  orbital  cavity,  espe- 
cially when  it  is  upon  the  external  side,  will  particularly  paralyze  the 
abducent.  Unilateral  paralyses  of  this  nerve  are  usually  of  peripheral 
origin.  Bilateral  paralysis  is  generally  due  to  central  disturbance. 
The  most  prominent  symptom  of  this  affection  is  an  internal  or  con- 
vergent strabismus.  The  eye  is  held  inward  by  the  tenacity  of  the 
rectus  internus,  so  that  not  more  than  one  part  of  the  cornea  is  per- 
ceived. 

CONJUGATE  DEVIATION. 

Waller  explains  this  as  follows :  The  two  eyes  are  exactly  equal 
and  parallel  for  different  directions  of  distant  vision.  Both  eyes  are 
turned  to  the  right  or  to  the  left,  up  or  down,  so  that  the  object  fixed 
gives  images  on  corresponding  parts  of  both  retinas.  In  movements 
directly  upward  or  downward  muscles  of  the  same  name  in  each  eye 
are  associated  in  action;  but  in  lateral  movements  the  association  is 
asymmetrical:  e.g.,  the  external  rectus  of  one  eye  acts  with  the  in- 
ternal rectus  of  the  other,  and  the  peculiarity  of  this  associated  action 
seems  still  more  striking  when  it  is  remembered  that  the  external 
rectus  is  supplied  by  the  sixth  nerve,  while  the  internal  rectus  is 


CRANIAL  NERVES.  537 

supplied  by  the  third.  A  similar,,  if  less  striking,  association  of 
asymmetrical  muscles  on  the  two  sides  occurs  in  the  rotation  of  the 
head  and  neck,  which  are  turned  to  the  right  by  the  right  inferior 
oblique  and  the  left  sterno-mastoid  muscles,  and  to  the  left  by  the 
left  inferior  oblique  and  the  right  sterno-mastoid.  In  looking  to  the 
right  we  contract  the  right  external  and  left  internal  rectus:  i.e., 
impulses  pass  through  the  right  sixth  nerve  and  the  left  third,  pos- 
sibly from  the  left  and  from  the  right  side,  respectively,  of  the  motor 
cortex,  but  more  probably  from  only  the  left  motor  cortex,  in  which 
case  we  must  suppose  that  certain  nerve-fibers  cross  twice:  once 
between  the  cortex  and  bulbar  nucleus  and  a  second  time  between 
the  nucleus  and  nerve-termination.  Unilateral  convulsions  of  cor- 
tical origin  are  accompanied  by  rotation  of  the  head  and  eyes  toward 
the  convulsed  side:  i.e.,  away  from  the  cerebral  lesion.  Thus  a 
discharging  lesion  of  the  right  motor  cortex  causes  convulsions  of 
the  left  side  of  the  body,  with  rotation  of  the  eyes  to  the  left.  This 
is  a  "conjugate  deviation."  A  destructive  lesion  of  the  right  motor 
cortex  causes  paralysis  of  the  left  side  of  the  body,  with  rotation  of 
the  eyes  to  the  right.  The  peculiarity  in  this  case  is  that  there  is  a 
cessation  of  action  along  the  left  sixth  nerve  (external  rectus)  and 
the  right  third  nerve  (internal  rectus),  the  deviation  of  the  eyes  to 
the  right  being  caused  by  the  unbalanced  action  of  the  muscles,  which 
rotate  the  eyes  to  the  right. 

FIFTH  PAIR,  TRIGEMINUS,  OR  TRIFACIAL  NERVE. 

The  fifth  pair  of  nerves,  like  a  spinal  nerve,  has  two  roots:  an 
anterior  motor  one  and  a  posterior  sensory  one.  The  neuraxons  of 
the  motor  nucleus  in" the  pons  make  up  the  motor  root.  The  sensory 
arises  in  the  Gasserian  ganglion,  and,  like  a  posterior-root  ganglion, 
its  neuraxons  are  divided,  one  part  going  to  the  skin  of  the  face  and 
the  other,  running  toward  the  pons,  also  divides  into  two  parts,  one 
going  upward  and  the  other  downward.  The  gelatinous  substance  of 
Rolando  on  the  posterior  horn  receives  the  fibers  running  upward, 
which  arborize  around  the  cells. 

The  descending  part  of  the  trigeminus,  known  as  the  ascending 
root,  extends  down  to  the  second  cervical  vertebra,  continually  giving 
off  collaterals  as  it  descends,  which  arborize  around  the  gelatinous 
substance  of  Eolando  of  the  posterior  horn,  thus  making  the  lower 
trigeminal  nucleus  a  long  one.  The  descending  branch  also  has  col- 
laterals, which  arborize  around  the  motor  nuclei  of  the  hypoglossal, 
facial,  and  trifacial.  The  neuraxons  of  the  sensory  nuclei  in  which 


538  PHYSIOLOGY. 

the  trigemimis  ends  decussate  and  go  to  the  cortex  in  the  fillet.  The 
nucleus  of  the  motor  root  lies  in  the  pons,  near  the  sensory  nucleus 
of  the  trigeminus  and  back  of  the  nucleus  of  the  facial,  of  which  it 
is  probably  a  part.  There  is  another  nucleus,  the  accessory  nucleus 
of  the  motor  nucleus,  which  is  situated  beneath  the  aqueduct  of 
Sylvius,  and  which  sends  descending  fibers  to  the  motor  nucleus. 

The  trigeminus  emerges  from  the  pons  by  two  roots:  a  large 
sensory  root  and  a  small  motor  root.  The  large  root  has  the  Gas- 
serian,  or  semilunar,  ganglion,  while  the  small  root  runs  beneath  it. 
From  the  semilunar  ganglion  emanate  the  ophthalmic,  superior  max- 
illary, and  a  third  branch,  which  joins  the  small  root  of  the  trifacial 
to  form  the  inferior  maxillary  nerve.  The  nasal  branch  of  the 
ophthalmic,  ciliary,  or  lenticular,  ganglion,  gives  off  the  ciliary 
nerves  for  the  ciliary  muscle  and  iris.  This  ganglion  receives  motor 
fibers  from  the  oculomotor  nerve  and  branches  from  the  sympathetic. 
The  superior  maxillary  branch  passes  through  the  rotund  foramen 
of  the  sphenoid  bone  and  gives  off  dental  and  spheno-palatine  nerves 
which  go  to  MeckePs,  or  the  spheno-palatine,  ganglion.  It  gives 
off  nasal,  palatine,  and  pterygoid  nerves.  The  pterygoid  nerve 
gives  off  a  branch,  the  great  petrosal,  which  enters  the  cranial  cavity 
through  the  cavity  of  the  foramen  lacerum  and  enters  a  canal  on  the 
front  of  the  petrous  portion  of  the  temporal  bone  to  join  the  facial 
nerve.  The  inferior  maxillary  nerve  is  formed  of  the  small  motor 
root  of  the  trigeminus  and  a  third  branch  of  the  semilunar  ganglion, 
and  makes  its  exit  from  the  skull  by  the  oval  foramen.  It  gives  off 
the  auriculo-temporal  and  the  lingual  nerve,  which  in  its  course  is 
joined  by  the  chorda  tympani  of  the  facial  and  the  inferior  dental 
nerves.  On  the  sensory  division  of  the  inferior  maxillary  nerve  is 
seated  the  otic,  or  ganglion  of  Arnold.  From  it  emanates  the  small 
petrosal  nerve,  which  enters  the  cranium  through  a  fine  canal  in  the 
spinous  process  of  the  sphenoid  bone  and  then  courses  along  a  canal 
in  front  of  the  petrous  portion  of  the  temporal  bone  to  join  the  facial. 
The  otic  ganglion  gives  out  filaments  to  the  tensor  palati  and  tensor 
tympani  muscles. 

Physiology. — From  the  point  of  view  of  general  sensibility  the 
trigeminus  possesses  a  considerable  domain.  To  it  alone  is  intrusted 
the  giving  of  general  sensibility  to  nearly  all  parts  which  enter  into 
the  composition  of  the  head.  In  the  external  covering  of  the  head 
but  one  region  escapes  it,  which  is  the  lateral  and  posterior  part  of 
the  hairy  scalp,  the  innervation  for  the  latter  coming  from  the  cer- 
vical nerves. 


CRANIAL  NERVES.  539 

As  to  mucous-membrane  sensibility,  trifacial  innervation  comes 
only  to  the  posterior  third  of  the  tongue,  where  the  glosso-pharyngeal 
innervates  the  palate,  with  the  middle  and  inferior  parts  of  the 
pharynx. 

These  points  being  eliminated,  it  gives  tactile  sensibility  not  only 
to  the  skin,  but  also  to  all  of  the  tissues  of  the  head,  comprising  the 
glands,  meninges,  organs  of  sense,  bone,  and  dental  pulp. 

Reflex  Relations. — By  reason  of  the  ciliary  filaments  the  trigem- 
inus  is  in  particular  reflex  relation  with  the  motor  oculi  and  sympa- 
thetic. Because  of  the  ramifications  of  the  trifacial  branches  in  the 
mucous  membrane  of  the  nose  there  is  established  a  very  intimate 
relation  with  the  expiratory  muscles  and  nerves.  Even  the  slightest 
touch  may  occasion  a  sudden  and  violent  sneeze.  A  close  relationship 
exists  between  this  nerve  and  the  muscles  and  nerves  of  deglutition. 

A  remarkable  fact  in  connection  with  the  trigeminus  is  its  great 
functional  resistance  to  various  poisons  which  are  capable  of  paralyz- 
ing nerves  of  sensation.  While  all  other  regions  of  the  body  show 
the  effects  of  anaesthetics,  those  under  the  dominion  of  the  trigem- 
inus still  preserve  a  high  degree  of  sensibility.  Even  though  a  patient 
be  anesthetized  with  chloroform,  yet  will  he  perceive  punctures  in 
the  temples  and  frontal  regions.  This  occurs  in  spite  of  the  fact  that 
sensations  are  not  perceived  elsewhere. 

Motor  Functions. — By  its  short  root  the  trigeminus  holds  under 
its  power  the  movements  of  elevation,  depression,  and  rotation  of  the 
lower  jaw.  If  this  root  be  cut,  it  is  found  that  the  muscles  concerned 
in  the  performance  of  the  above-mentioned  movements  are  paralyzed. 
The  lower  jaw  remains  passively  separated  from  the  upper. 

Trophic  Function. — Within  twenty-four  hours  after  intracranial 
section  of  the  trigeminus,  the  cornea  becomes  opaque.  At  the  end 
of  five  or  six  days  the  cornea  becomes  very  white  in  color.  The  iris 
becomes  inflamed  and  covered  with  false  membranes.  In  about  eight 
days  the  cornea  becomes  detached  and  the  contents  of  the  eye  escape. 

The  suppression  of  the  fifth  pair  is  followed  by  remarkable 
alterations  in  the  Schneiderian  membrane.  It  becomes  spongy  and 
bleeds  upon  the  least  touch.  The  place  where  the  olfactory  bulbs  lie 
is  completely  changed.  Thus  the  acts  of  olfaction  and  vision  are 
indirectly  affected. 

Pathology. — By  reason  of  the  intimate  association  of  the  tri- 
geminus, and  its  Gasserian  ganglion,  with  the  petrous  portion  of  the 
temporal  bone,  it  is  exposed  to  all  of  the  shocks  and  blows  that  are 
able  to  fracture  this  bone. 


540  PHYSIOLOGY. 

The  relations  of  the  trigemimis  with  its  meninges  are  very  apt 
to  be  disturbed  seriously  by  the  presence  of  tumors.  The  false  mem- 
branes which  are  found  in  meningitis  compress  it  and  so  produce 
atrophy.  The  exudates  of  tubercular  meningitis  very  often  produce 
anaesthesia  of  the  face. 

The  fifth  pair  is  most  often  the  seat  of  either  excessive  sensibil- 
ity or  paralysis.  It  is,  perhaps,  the  one  nerve  which  is  the  most 
frequently  affected  in  neuralgia.  The  relative  nearness  of  the  tri- 
geminus  to  its  sensory  center  probably  explains  the  acuteness  of  the 
pains  in  neuralgia. 

SEVENTH  PAIR,  FACIAL  NERVE,  OR  PORTIO  DURA. 

The  facial  nerve  arises  from  a  nucleus  beneath  the  floor  of  the 
fourth  ventricle.  This  nerve  contains  a  motor  and  a  sensory  root. 
The  sensory  root  comes  from  the  cells  of  the  geniculate  ganglion,  and 
is  called  the  nerve  of  Wrisberg.  The  motor  pontal  nucleus  gives  off 
the  neuraxons  of  the  motor  root.  The  motor  nucleus  is  thought  to  be 
the  upward  part  of  the  nucleus  ambiguus,  which  originates  the  motor 
fibers  in  the  vagus  and  glosso-pharyngeal  nerves.  The  neuraxons  of 
the  motor  nucleus  form  a  distinct  knee,  which,  uprising  on  the  floor 
of  the  fourth  ventricle,  is  known  as  the  eminentia  teres.  The  facial 
nerve  in  its  course  to  the  periphery  makes  a  peculiar  loop,  or  knee, 
inclosing  the  nucleus  of  the  abducent,  and  emerges  from  a  depression 
back  of  the  pons  between  the  olivary  and  restiform  bodies,  enters  the 
internal  auditory  meatus  with  the  auditory  nerve,  leaves  the  auditory 
nerve,  enters  the  Fallopian  canal,  and  makes  its  exit  by  the  stylo- 
mastofd  foramen  to  go  to  the  muscles  of  the  face.  The  nerve  of  Wris- 
berg, or  the  sensory  part  of  the  facial,  is  made  up  of  neuraxons  from 
the  cells  of  the  geniculate  ganglion  seated  in  the  Fallopian  canal. 
The  auditory  nerve  is  also  called  portio  mollis,  and  it  lies  to  the  outer 
side  of  the  facial, — the  portio  dura, — and  between  the  two  is  the 
pars  intermedia  portio  inter  duram  et  mollem  of  Wrisberg,  which 
extends  from  the  medulla  to  join  the  facial  in  the  internal  auditory 
meatus.  It  is  connected  with  both  auditory  and  facial  nerves,  be- 
tween which  it  lies.  The  central  neuraxons  of  the  geniculate  gan- 
glion or  the  nerve  of  Wrisberg  go  to  the  fasciculus  solitaries  or  the 
vagus  and  glosso-pharyngeal  roots.  The  peripheral  neuraxons  of  the 
geniculate  ganglion  join  the  facial,  and  Duval  states  that  they  go  to 
form  the  nerve  of  taste :  the  chorda  tympani. 

In  the  hiatus  Fallopii  the  great  petrosal  nerve  branches  off  from 
the  facial.  It,  in  conjunction  with  a  filament  from  the  glosso-pharyn- 


CRANIAL  NERVES.  541 

geal  and  another  from  the  sympathetic,  passes  over  to  join  the  gan- 
glion of  Meckel. 

The  small  petrosal  leaves  the  aqueduct  by  a  particular  opening  to 
end  in  the  otic  ganglion. 

Chorda  Tympani. — A  few  millimeters  above  the  stylo-mastoid 
foramen  the  facial  gives  off  a  branch  of  very  considerable  size:  the 
chorda  tympani.  It  ascends  into  the  cavity  of  the  tympanum.  It 
passes  between  the  malleus  and  incus,  giving  a  branch  to  the  lat- 
ter, and  then  enters  the  zygomatic  fossa.  The  chorda  tympani  then 
descends  between  the  two  pterygoid  muscles  to  meet  the  nerve  of 
taste.  After  communicating  with  the  latter  it  accompanies  it  to  the 
submaxillary  gland.  There  it  joins  the  submaxillary  ganglion  to 
terminate  in  the  lingual  nerve. 

Physiology. — While  the  trigeminus  is  responsible  for  the  sensory 
actions  of  the  face,  the  facial  presides  over  the  contraction  of  the 
facial  muscles  of  expression. 

The  facial  nerve  is  purely  motor,  and  so  has  nothing  to  do  with 
the  transmission  of  sensory  impressions  developed  upon  the  face. 
After  its  section  the  skin  still  preserves  all  of  its  sensibility.  On 
the  other  hand,  after  section  of  the  trifacial  it  completely  disappears. 
Though  the  facial  does  not  transmit  sensory  impressions,  yet  in  itself 
it  is  sensitive  because  of  the  branches  which  it  receives  from  the 
trigeminus.  If  the  nerve  be  pinched,  the  animal  shows  signs  of  pain. 

Pathology. — The  facial  is  the  motor  nerve  which  suffers  most 
easily  from  the  influence  of  cold.  Facial  paralysis,  or  Bell's  palsy,  may 
occur  very  easily  when  draughts  from  a  window  blow  upon  the  face. 

When  the  paralysis  is  unilateral,  the  face  is  drawn  toward  the 
sound  side.  The  labial  commissure  on  the  paralyzed  .side  is  lower 
than  the  other,  thus  giving  to  the  mouth  an  oblique  direction. 

BelPs  paralysis  is  usually  due  to  a  cold  draught  of  air  striking 
the  nerve  at  its  exit  from  the  stylo-mastoid  foramen.  When  the 
cause  is  seated  in  the  brain  the  external  rectus  is  usually  affected, 
because  its  nerve  is  also  involved  and  usually  there  is  paralysis  of  the 
opposite  half  of  the  body,  or  crossed  paralysis.  Here  the  lesion  is  in 
the  pons.  If  the  lesion  is  seated  in  the  petrous  portion  of  the  tem- 
poral bone,  there  is  not  only  facial  palsy,  but  also  loss  of  taste  from 
an  involvement  of  the  chorda  tympani. 

EIGHTH   PAIR,  OR  AUDITORY  NERVE. 

The  anatomy  and  function  of  this  nerve  have  been  discussed  in 
Chapter  XVIII. 


542  PHYSIOLOGY. 

NINTH   PAIR,   OR   GLOSSO=PHARYNGEAL   NERVE. 

The  glosso-pharyngeal  nerve  is  a  nerve  of  both  motion  and  sen- 
sation. The  nucleus  ambiguus  gives  off  neuraxons  to  form  its  motor 
root.  The  sensory  neuraxons  arise  from  the  jugular  and  petrosal 
ganglions  and  arborize  about  two  sensory  nuclei  in  the  medulla  ob- 
longata.  The  lower  sensory  end  nucleus  produces  an  elevation  on 
the  floor  of  the  fourth  ventricle,  and  is  called  the  ala  cinerea.  The 
upper  nucleus  is  also  connected  with  sensory  neuraxons  of  glosso- 
pharyngeal  nerves,  while  the  lower  portion  of  this  nucleus  is  in 
relation  with  the  vagus.  The  second  nucleus  is  called  the  vertical 
nucleus,  the  fasciculus  solitarius,  the  combined  descending  root  of 
the  pneumogastric  and  glosso-pharyngeal  nerves,  or  the  respiratory 
bundle.  This  respiratory  tract  extends  from  the  olive  down  the  spine 
to  the  eighth  cervical  nerve.  This  respiratory  bundle  of  Gierke  may 
associate  the  nuclei  co-ordinating  the  various  respiratory  muscles. 
The  glosso-pharyngeal  nerve  arises  by  a  half-dozen  cords  from  the 
restiform  body  and  goes  through  the  jugular  foramen  into  the  vagus, 
where  it  has  a  small  ganglion :  the  jugular.  As  it  emerges  from  the 
jugular  foramen  there  is  developed  the  petrosal  ganglion,  or  ganglion 
of  Andersch. 

Nerve  of  Jacobson. — This  same  ganglion  gives  origin  to  the  nerve 
of  Jacobson.  It  enters  the  cavity  of  the  tympanum  by  way  of  an 
opening  in  its  floor,  where  it  divides  into  three  filaments.  These  are 
distributed :  one  to  the  round  window,  one  to  the  oval  window,  the 
third  to  the  lining  membrane  of  the  Eustachian  tube  and  tympanum. 

Physiology. — The  ninth  is  a  mixed  nerve.  Its  motor  properties 
are  distributed  to  the  middle  constrictors  of  the  pharynx  and  the 
stylo-pharyngeus  muscle. 

The  most  important  sensory  function  of  the  glosso-pharyngeal 
is  the  part  which  it  plays  in  the  role  of  the  sense  of  taste. 

The  ninth  nerve  has  an  action  upon  the  blood-vessels  of  the 
tongue  identical  with  that  of  the  chorda  tympani.  If  the  glosso- 
pharyngeal  be  cut  and  its  peripheral  end  stimulated,  the  tongue 
becomes  of  a  livid  red. 

Pathology. — In  man  there  are  no  clear  cases  recorded  where 
there  have  been  uncomplicated  affections  of  the  glosso-pharyngeal. 

TENTH  PAIR,  PNEUMOGASTRIC,  OR  VAGUS. 

Of  all  of  the  cranial  nerves,  the  vagus  is  the  most  important  and 
has  the  most  functions  of  a  varied  nature  in  clinical  study.  It  is  a 


CEANIAL  NERVES.  543 

nerve  of  motion  and  sensation.  The  motor  neuraxons  arise  from 
the  nucleus  ambiguus.  The  sensory  roots  come  from  the  neuraxons 
of  the  jugular  and  petrosal  ganglions.  The  sensory  neuraxons  have 
been  described  under  the  preceding  nerve:  the  glosso-pharyngeal. 
The  vagus  springs  by  means  of  from  ten  to  fifteen  cords  from  the 
groove  behind  the  olivary  body  and  passes  through  the  jugular  fora- 
men with  the  glosso-pharyngeal  and  spinal  accessory  nerves.  In  the 
jugular  foramen  it  has  a  ganglion:  the  jugular  ganglion.  After  it 
emerges  from  the  foramen  it  has  an  enlargement,  the  gangliform 
plexus,  or  ganglion  nodosum. 

The  plexus  gives  off  the  pharyngeal  and  superior  laryngeal  nerves. 

The  pharyngeal  nerves,  three  in  number,  go  down  the  side  of  the 
pharynx  to  supply  the  mucous  membrane  and  muscles  of  the  pharynx. 
The  superior  laryngeal  goes  down  the  side  of  the  larynx.  This  nerve 
also  furnishes  a  collateral  branch,  important  from  a  physiological 
standpoint,  to  the  crico-thyroid  muscle.  It  then  loses  itself  in  the 
mucous  membrane  of  the  larynx. 

At  the  base  of  the  neck  the  vagus  gives  off  another  branch,  the 
recurrent,  or  inferior  laryngeal.  The  nerve  upon  the  right  side  de- 
scends in  front  of  the  subclavian  artery  and  winds  around  it  pos- 
teriorly from  beneath.  Upon  the  left  side  the  nerve  winds  around 
the  arch  of  the  aorta  in  the  same  manner. 

As  collateral  branches,  the  vagus  furnishes  cardiac  fibers,  which 
form  the  cardiac  plexus  and  are  destined  to  innervate  the  heart. 
There  are  also  oesophageal  fibers  whose  terminations  are  distributed 
to  the  oesophagus  and  trachea. 

In  the  cervical  region  the  tenth  pair  gives  rise  to  a  branch,  the 
nervus  depressor.  It  results  by  the  fusion  of  two  fibers:  one  from 
the  superior  laryngeal  and  the  other  from  the  vagus  itself.  The 
nervus  depressor  loses  itself  in  the  cardiac  tissue  of  the  heart  at 
the  level  of  the  aortic  and  pulmonary  orifices. 

During  the  first  portion  of  its  course  the  vagus  forms  numerous 
anastomoses.  These  are  with  the  spinal  accessory,  the  facial,  and 
hypoglossal  cranial  nerves,  and  with  a  great  number  of  branches  from 
the  various  ganglia  of  the  sympathetic  system. 

In  the  thorax  the  vagus  gives  off  cardiac  and  pulmonary  branches. 
These  also  anastomose  with  the  sympathetics  to  form  numerous 
plexuses. 

The  terminal  branches  of  the  vagus  are  distributed  to  the  stom- 
ach., to  the  solar  plexus,  and  also  to  the  hepatic  plexus  of  the  sympa- 
thetic. 


544  PHYSIOLOGY. 

The  most  striking  feature  with  regard  to  the  vagus  is  the  great 
number  of  its  anastomoses.  It  is  a  very  complex  nerve  and  in  no 
part  of  its  course  is  it  exclusively  itself. 

Physiology. — The  relationship  existing  between  the  vagus  and 
spinal  accessory  nerves  is  a  very  intimate  one  by  reason  of  their 
anastomoses.  This  makes  the  determination  of  the  true  nature  of 
the  vagus  one  of  the  difficult  problems  of  physiology. 

It  is  certain  that  the  vagus  is  endowed  with  sensibility,  for  the 
suppression  of  the  spinal  accessory  does  not  deprive  the  parts  of  any 
sensibility  in  any  portion  of  their  common  distribution.  But,  as  the 
spinal  accessory  is  motor  and  the  vagus  sensory,  it  does  not  neces- 
sarily follow  that  the  latter  nerve  is  exclusively  sensory  and  that  all 
movements  realized  by  association  should  be  the  special  work  of  the 
spinal  accessory.  It  was  Bernard  who  first  demonstrated  that  the 
vagus  in  itself  is  a  mixed  nerve.  After  he  had  torn  out  all  of  the  root- 
fibers  of  the  spinal  accessory  in  animals  he  found  that  the  motor 
acts  of  the  larynx  persisted  in  the  phenomena  of  respiration.  How- 
ever, while  the  vagus  in  itself  is  a  mixed  nerve  and  has  a  certain 
amount  of  motor  functions,  yet  its  principal  role  is  of  a  sensory 
nature. 

The  mode  of  distribution  of  the  vagus  indicates  that  the  nerve 
exercises  some  action  upon  (1)  the  digestive  apparatus,  (2)  the  respira- 
tory apparatus,  (3)  the  circulation,  (4)  the  hepatic  apparatus,  and 
(5)  an  indirect  action  upon  the  kidneys  and  suprarenal  glands. 

Pathology. — The  recurrent  is  more  liable  to  be  pressed  upon  by 
reason  of  its  peculiar  course  and  its  direct  relations  with  the  great 
vessels  and  bod}r  of  the  thyroid.  As  the  vagus  is  a  mixed  nerve,  it 
is  very  evident  that  compression  causes  troubles  in  motion  and  sensi- 
bility, either  isolated  or  conjointly. 

Any  lesions  located  at  the  origin  of  the  vagus  cause  phenomena 
of  irritation  in  the  whole  sphere  of  distribution  of  this  nerve.  Ee- 
flexly  the  vagus  is  capable  of  affecting  the  chorda  tympani  and  in- 
creasing the  flow  of  saliva.  It  is  for  this  reason  that  intestinal 
parasites  often  cause  ptyalism. 

The  sensibility  of  the  branches  of  the  vagus  in  the  stomach  re- 
mains unconscious  during  the  normal  physiological  state,  when  it 
does  not  seem  to  be  any  greater  than  that  of  the  sympathetic.  Dur- 
ing pathological  conditions,  however,  it  acquires  a  high  degree  of 
intensity.  Thus,  in  simple  wounds  of  the  stomach,  without  haemor- 
rhage or  peritonitis,  the  impression  carried  to  the  medullary  center 
may  be  of  such  a  nature  as  to  cause  rapid  death. 


CRANIAL  NERVES.  545 

The  great  frequency  of  gastralgia  is  due  to  an  affection  of  the 
terminal  branches  of  the  tenth  pair.  At  its  cranial  end  this  same 
nerve  is  found  to  be  in  direct  relation  with  the  trigeminus  through 
the  intervention  of  the  gray  tubercle  of  Rolando.  This  fact  un- 
doubtedly furnishes  the  key  to  the  headache  which  so  often  accom- 
panies gastralgia. 

The  vagus  is  the  chief  sensory  carrier  of  the  reflex  movements 
of  circulation  and  respiration.  Thus,  irritation  of  the  renal  and 
hepatic  plexuses  can  produce  vomiting. 

Angina  pectoris  has  its  seat  in  the  cardiac  plexus.  The  sensation 
experienced  is  like  that  seen  in  the  renal  and  hepatic  plexuses  after 
renal  and  hepatic  colic. 

ELEVENTH  PAIR,  OR  SPINAL  ACCESSORY  NERVE. 

The  eleventh  pair  of  cranial  nerves,  the  spinal  accessory,  is  com- 
posed of  two  distinct  parts :  a  spinal  portion  and  an  accessory  portion. 
A  group  of  cells  in  the  anterior  horns  of  the  spinal  cord  and  extend- 
ing downward  to  the  sixth  cervical  segment  is  called  the  accessory 
nucleus.  There  is  another  group  of  cells  at  the  exit  of  the  first 
cervical  nerve  which  extends  into  the  medulla  oblongata  and  is  the 
origin  of  the  hypoglossal  nerve.  The  medulla-oblongata  root  arises 
from  the  nucleus  ambiguus,  which  is  connected  with  the  vagus 
nucleus  in  the  medulla. 

The  superficial  origin  of  the  accessory  portion  is  from  the  groove 
between  the  inferior  olive  and  the  restiform  body.  Near  the  jugular 
foramen  both  portions  come  together,  but  do  not  exchange  fibers. 
Very  soon  both  roots  separate  from  one  another  to  form  the  two 
distinct  branches. 

The  accessory  portion  of  the  nerve  passes  entirely  into  the  plexus 
gangliformis  of  the  vagus.  This  branch  supplies  the  vagus  with  the 
major  portion  of  its  motor  fibers  and  also  with  its  cardio-inhibitory 
fibers. 

The  spinal  portion  enters  the  cavity  of  the  cranium  by  passing 
through  the  foramen  magnum.  The  two  portions  of  the  spinal 
accessory  leave  the  cranium  together  by  passing  through  the  middle 
compartment  of  the  jugular  foramen.  The  spinal  portion  then 
pierces  the  sterno-mastoid  to  supply  it  and  the  trapezius.  This  por- 
tion of  the  nerve  communicates  with  several  cervical  nerves. 

Physiology. — The  eleventh  nerve  is  generally  considered  to  be 
motor.  Any  observable  sensibility  must  be  due  to  anastomosis  with 
the  cervical  nerves. 


546  PHYSIOLOGY. 

From  experimentation  it  has  been  found  that  the  accessory  branch 
presides,  through  branches  in  the  vagus,  over  the  formation  of  sound 
and  its  tone.  The  spinal  branch  is  concerned  in  the  duration,  in- 
tensity, and  modulation  of  the  vocal  sound.  Hence  it  regulates  the 
rhythm  of  speech  and  song. 

Aphonia  is  often  due  to  hysteria,  but  may  be  due  to  lead  poisoning, 
syphilis,  or  to  such  reflex  causes  as  intestinal  worms.  The  reflex 
that  is  established  between  the  vocal  and  genital  organs  is  also 
shown  by  troubles  in  the  spinal  branch  of  the  spinal  accessory.  The 
voice  may  be  lost  at  times  during  menstruation. 

TWELFTH  PAIR,  OR  HYPOGLOSSAL  NERVE. 

The  nuclei  of  the  hypoglossal  nerve  are  under  the  floor  of  the 
fourth  ventricle,  on  each  side  of  the  raphe.  Beneath  the  main  nucleus 
of  the  hypoglossal  nerve  is  a  collection  of  cells  in  the  formatio 
reticularis  called  the  hypoglossal  nucleus  of  Boiler. 

Anastomoses. — The  connections  of  the  hypoglossal  are:  1.  With 
the  superior  -cervical  ganglion  of  the  sympathetic,  which  supplies 
vasomotor  fibers  to  the  vessels  of  the  tongue.  2.  The  plexus  gangli- 
formis  vagi  gives  a  small  lingual  branch  which  supplies  the  tongue 
with  sensory  fibers.  3.  The  hypoglossal  is  also  connected  with  the 
upper  cervical  nerves. 

Physiologyv — The  hypoglossus,  by  itself,  is  purely  motor.  It 
moves  the  muscles  of  the  tongue.  When  its  original  filaments  are 
torn  out  there  is  never  any  pain.  Sensibility  of  its  terminal  branches 
is  due  to  anastomoses  with  the  lingual.  When  the  hypoglossus  is  cut, 
the  tongue  remains  quiescent  in  the  mouth. 

In  unilateral  paralysis  of  the  hypoglossus  the  tongue,  when  pro- 
truded, passes  over  to  the  paralyzed  side.  This  phenomenon  is  occa- 
sioned by  the  action  of  the  genio-hyoglossus  of  the  sound  side. 

LITERATURE  CONSULTED. 

Gordinier,  "Nervous  System." 


CHAPTER  XXI. 

REPRODUCTION. 

REPRODUCTION,  with  the  aim  to  maintain  the  species,  is  one  of 
Nature's  foremost  laws.  On  every  side  of  us  does  biology  demon- 
strate this  to  the  student.  It  is  foremost  in  all  the  varying  stages  of 
both  animal  and  vegetable  life:  from  the  lowest  organisms  to  the 
highest.  Among  the  amoebae  and  other  forms  of  lower  life  are  their 
own  definite  laws  of  reproduction  adhered  to  and  carried  out  as  per- 
fectly as  among  the  highest  order  of  the  vertebrata. 

THE  LOWER  ORDERS. 

Among  the  lower  orders  of  creation  there  is  not  present  that 
great  complexity  and  amount  of  detail  seen  in  the  reproduction  of  the 
higher  orders.  The  individuals  of  the  lowest  orders,  whether  plant 
or  animal,  seem  to  possess  in  their  every  part  and  component  the 
general  plan  of  that  particular  species  of  plant  or  animal.  And, 
furthermore,  each  part  and  component  is  capable  of  building  up  for 
itself  a  perfect  plant  or  animal.  It  is  not  necessary  for  its  propaga- 
tion that  there  be  specialized  cells  present,  or  that  it  be  aided  by 
other  and  perfect  individuals  of  its  own  species. 

It  has  long  been  known  that,  should  a  portion  of  a  hydra  be 
separated  from  the  living  animal,  it  will  develop  into  a  complete 
hydra. 

The  agriculturist  makes  use  of  the  fact  that  from  a  cutting, 
branch,  tuber,  or  even  a  leaf  of  a  plant  there  may  spring  a  perfect 
plant  of  the  exact  species  from  which  the  parts  were  taken. 

Among  the  lowest  organisms  there  is  no  need  for  sex  or  special- 
ized cells  by  whose  union  there  emanates  an  entirely  new  individual. 
There  are  present  in  every  part,  and,  in  fact,  within  the  cells  of  every 
part,  those  inherent  principles  which  are  the  essentials  for  the  proper 
reproduction  of  the  individual. 

AMONG  HIGHER  ANIMALS. 

Among  the  higher  animals  the  plan  of  the  entire  organism  is  not 
latent  in  each  and  every  portion  of  its  economy.  Any  portion  that 
is  severed  from  the  individual  promptly  dies,  unless  it  be  properly 
nourished  and  cared  for.  Among  these  higher  spheres  of  life  sex 

(547) 


548  PHYSIOLOGY. 

is  a  most  important  factor  in  reproduction.  The  two  sexes  are  sepa- 
rate. In  order  that  a  new  being  be  brought  into  existence,  it  becomes 
necessary  that  specialized  cells  of  the  male  be  brought  into  conjunc- 
tion with  specialized  cells  of  the  female:  that  is,  fecundation,  or 
impregnation,  must  occur. 

Fractional  Reproduction. 

By  the  term  "  reproduction  "  is  generally  conveyed  the  idea  that 
there  is  propagation  of  the  species  by  the  formation  of  an  entirely 
new  individual.  However,  the  fact  must  not  be  lost  sight  of  that, 
among  the  higher  orders,  there  occurs  a  reproduction,  to  a  certain 
limited  extent,  of  the  various  components  of  the  organism:  a  frac- 
tional reproduction,  so  to  speak. 

From  the  incessant  wear  and  tear  incident  to  almost  constant 
usage,  the  various  components  of  the  economy  are  losing  many  of 
their  cells  by  death.  These  dead  cells,  no  longer  able  properly  to 
functionate,  find  egress  from  the  body.  To  maintain  a  normal  and 
well-balanced  body  it  is  necessary  that  the  wasted,  ejected  cells  be 
renewed.  Hence,  during  the  natural  cycle  of  the  animaPs  life  there 
is  constantly  occurring  a  partial,  or  fractional,  reproduction  of  the 
economy's  organs.  When  the  tissues  of  any  organ  are  not  too  highly 
specialized  this  reproduction  is  very  evident,  as  new  skin  covering  an 
ulcerous  area  by  means  of  granulation  tissue.  On  the  other  hand, 
nerve-cells,  which  are  representatives  of  the  highest  type  of  spe- 
cialized tissue,  are  not  believed  to  be  reproduced.  Lesions  among 
these  cells  are  healed  by  granulation  and  cicatricial  tissue. 

Among  some  animals  this  partial  reproduction  is  more  marked 
than  in  men  and  other  high  types  of  animal  life.  It  is  said  that  in 
the  hydra  an  amputated  part  is  replaced,  not  by  cicatricial  tissue,  but 
by  the  regular  specialized  tissues  as  they  occur  in  the  animal. 

Fecundation. 

As  just  stated,  it  is  necessary  that  the  male  elements  enter  into 
conjunction  with  the  female  element  before  fecundation  takes  place 
among  the  higher  animals.  The  male  specialized  element  is  the 
spermatozoon;  the  female,  the  ovum.  Both  of  these  sexual  cells  are 
the  results  or  products  of  a  series  of  changes  which  have  taken  place 
in  certain  epithelial  cells. 

Spermatozoon. — That  portion  of  the  seminal  fluid  which  comes 
from  the  testis  contains  myriads  of  microscopical  cells :  the  sperma- 
tozoa. These  little  bodies,  or  sexual  cells,  are  derivatives  of  the  wall> 


REPRODUCTION. 


549 


of  the  seminiferous  tubules.  The  tubules  are  lined  with  low-cuboidal 
cells  which  become  broken  up  so  as  to  form  spermatoblasts.  Each 
spermatoblast  by  further  metamorphosis  becomes  a  spermatozoon. 

STRUCTURE. — The  spermatozoa  of  various  animals  present  differ- 
ences as  to  shape  and  size.  The  human  spermatozoon  is  an  elongated, 
ciliarylike  body.  It  is  about  one-five-hundredth  of  an  inch  long  and 
presents  three  portions :  head,  middle  piece,  and  tail. 

The  head  is  the  most  prominent  portion  of  the  body  and  repre- 
sents the  nucleus  of  the  spermatozoon.  It  is  the  essential  portion  of 
the  spermatozoon  as  regards  sexual  function. 


V 

Fig.   136. — Human  Spermatozoa.     (MANTON.) 

The  tail  is  a  slender,  albuminous  filament  whose  chief  function 
seems  to  be  to  propel  the  cell  in  ita  search  for  the  female  element : 
the  ovum. 

Ovum. — The  ovum  is  a  small,  spheroidal  body  lodged  in  a  Graaf- 
ian  follicle  within  the  ovary  of  the  female.  It  is  the  female  sexual 
cell. 

In  size  the  human  ovum  measures  about  one  one-hundred-and- 
twentieth  of  an  inch  in  diameter.  Not  only  the  human  ovum,  but 
ova  of  other  animals  are  remarkable  in  that  they  are  larger  than  any 
other  cell  within  the  body  of  the  female. 

The  ovum  is  a  typical  cell,  containing  cell-wall,  cell-contents, 
nucleus,  and  nucleolus.  Like  other  cells,  it  undergoes  division  and 
produces  cells  which  ultimately  form  the  various  tissues  of  the  future, 


550  PHYSIOLOGY. 

but  not  before  the  ovum  has  been  fertilized  by  union  with  the  sper- 
matozoon. 

The  ovum  is  the  final  product  of  a  series  of  metamorphic  changes 
occurring  in  cells  which  have  been  derived  from  the  germinal  epithe- 
lium of  the  ovary.  Each  ovum  develops  within  its  own  compartment, 
a  Graafian  follicle;  as  the  ovum  nears  completion  the  follicle  moves 
to  the  surface  of  the  ovary.  The  fluid  contained  within  the  follicle 
then  gradually  thins  its  own  wall  as  well  as  the  germinal  epithelium 
of  the  ovary  until  there  occurs  a  rupture  of  the  sac.  The  ovum,  with 
the  escape  of  the  fluid,  also  passes  out  upon  the  surface  of  the  ovary. 

During  sexual  excitement  the  fimbriated  end  of  the  Fallopian 
tube  grasps  the  ovary,  and  the  ovum  is  conducted  to  the  tube  by  the 


Mg.  137.—  Ovum  of  Rabbit. 


fimbria  ovarica,  and  is  then  carried  through  the  tube  down  into 
the  uterus  by  the  instrumentality  of  the  ciliated  epithelium  lining  the 
tube.  This  escape  of  the  ovum^from  its  Graafian  follicle  is  known 
by  the  term  ovulation.  Should  the  ovum  not  be  impregnated,  it  dies 
and  passes  out  of  the  uterus  as  a  constituent  of  its  secretions.  On 
the  other  hand,  should  it  become  fecundated,  the  ovum  becomes  at- 
tached to  the  mucous  membrane  of  the  uterus,  usually  occupying  the 
bottom  of  some  little  cleft  or  pouch. 

The  investigations  of  Peters,  of  Vienna,  and  of  Webster,  of 
Chicago,  show  that  the  uterine  mucosa  does  not  fold  up  around  the 
ovum,  but  that  the  mucosa  at  the  site  of  implantation  is  eroded;  so 
that  the  ovum  eats  its  way,  as  it  were,  into  the  mucosa,  sinking  into 
its  depths  until  the  edge  of  the  swollen  mucosa  closes  over  it,  thus 
forming  the  decidua  reflexa. 


REPRODUCTION.  551 

MATUKATION. — Before  the  ovum  leaves  its  follicle  and  before 
it  is  possible  for  it  to  be  impregnated,  the  ovum  must  pass  through  the 
process  of  maturation,  or  ripening.  In  short,  the  process  is  the  expul- 
sion of  a  portion  of  the  nucleus  arid  protoplasm  of  the  ovum.  The 
nucleus  then  undergoes  changes  which  seem  to  be  the  same  as  those 
occurring  during  ordinary  karyokinesis.  The  significance  of  matura- 
tion is  believed  by  some  observers  to  be  to  furnish  room  in  the  ovum 
for  the  entrance  of  the  male  pronucleus,  which  is  to  occupy  the  place 
of  the  portion  lost. 

Menstruation. — In  the  adult  female  during  certain  age-limits 
there  occurs  a  discharge  from  the  genitalia  once  about  every  twenty- 
eight  days.  This  periodical  discharge  consists  of  blood,  dead  and 
disintegrated  epithelium  from  the  uterus,  and  mucus  from  the  glands 
of  the  uterus. 

With  the  discharge  of  the  above-named  materials  there  is  usually 
expelled  at  the  same  time  one  or  more  ova  from  their  follicles.  How- 
ever, ovulation  and  menstruation  may  be  and  very  often  are  inde- 
pendent of  one  another.  The  onset  of  menstruation  is  usually  her- 
alded and  then  accompanied  by  certain  constitutional  signs  of  fullness 
and  pain  in  the  pelvic  region.  There  is  a  real  congestion  of  all  of 
the  pelvic  organs;  in  particular  the  uterine  mucous  membrane  is 
swollen  and  congested.  From  it  are  derived  the  blood  and  epithelium 
of  the  menstrual  flux.  By  some  authorities  it  is  claimed  that  the 
entire  uterine  mucous  membrane  is  exfoliated  at  every  flux,  to  be 
regenerated  in  the  interim. 

It  has  been  found  by  observers  that  congestion  of  the  ovary 
coincident  with  sexual  intercourse  is  capable  of  rupturing  Graafian 
follicles  and  so  liberating  ova.  From  this  it  is  reasonable  to  suppose 
that  the  congestion  and  high  tension  of  the  generative  organs  during 
the  time  of  menstruation  would  surely  accomplish  the  same  end. 

The  usual  period  of  a  female's  life  during  which  she  menstruates 
is  from  puberty  (from  the  thirteenth  to  the  fifteenth  year)  to  the 
climacteric,  or  menopause  (about  the  forty-fifth  year.)  Its  cessation 
at  the  latter  period  denotes  the  end  of  the  childbearing  period. 

Fertilization, — This  is  the  proper  union  of  the  male  and  female 
sexual  cells  after  the  ovum  has  been  previously  matured,  or  ripened. 
The  act  is  consummated  when  the  head  of  the  spermatozoon  (now 
known  as  the  male  pronucleus)  becomes  permanently  fused  with  the 
remnant  of  the  nucleus  of  the  ovum  (the  female  pronucleus). 

Segmentation. — The  unimpregnated  ovum  soon  perishes;  not  so 
with  one  that  is  fertilized.  The  latter  immediately  begins  to  show 


552  PHYSIOLOGY. 

karyokinetic  changes,  segmentation  following  segmentation  until  the 
ovum  has  become  a  mass  of  cells :  the  morula.  These  are  the  prim- 
itive cells  from  which  all  of  the  tissues  of  the  future  embryo  are 
formed.  They  are  known  as  Hastomeres. 

During  segmentation  the  ovum  is  enlarging  by  the  absorption  of 
fluid  into  its  interior  and  the  formation  of  a  cleavage-cavity  in  the 
center  of  the  morula.  From  pressure  upon  one  another  the  cells 
become  polyhedral  in  shape  and  are  so  arranged  as  to  form  a  cellular 
envelope  just  inside  of  the  vitelline  membrane, — the  blastoderm, — and 
a  central  mass  of  cells  projecting  from  the  wall  into  the  cleavage- 
cavity. 

The  cells  forming  the  wall  of  the  cleavage-cavity,  known  as  the 
outer  cell-mass,  thin  out  and  are  known  as  the  cells  of  Kauber;  they 
subsequently  disappear,  while  the  cells  of  the  inner  cell-mass,  which 
later  projects  into  the  cleavage-cavity,  become  rearranged  in  a  man- 
ner at  present  inexplicable,  to  form  two  layers:  the  entoderm  and 
the  ectoderm,  respectively.  The  outer  layer  is  known  as  the  ectoderm? 
or  epiUast;  the  inner,  as  the  entoderm,  or  hypollast. 

Embryonal  Area. — At  the  beginning  of  the  stage  of  gastrulation 
there  appears  upon  the  delicate  vitelline  membrane  a  round,  whitish 
spot.  It  is  the  embryonal  area,  or  shield.  The  area  becomes  oval  and 
then  pear-shaped.  At  the  narrow  end  there  appears  an  elongated 
narrow  thickening:  the  primitive  streak.  Later  the  streak  develops  a 
furrow :  the  primitive  groove. 

At  the  same  time  there  appears  in  the  region  of  the  front  end 
of  the  primitive  streak  several  layers  of  new  cells.  As  they  occupy 
a  position  between  the  ectoderm  and  entoderm,  they  have  been  desig- 
nated the  mesoderm. 

While  the  mesoderm  is  pushing  its  way  over  the  germinal  area 
and  into  the  blastoderm,  the  epiblast  in  front  of  the  primitive  streak 
rises  up  so  as  to  form  two  lateral  ridges.  These  inclose  within  them 
the  medullary  groove.  Very  soon  the  edges  of  these  two  ridges  begin 
to  curl  up,  to  produce  the  medullary  canal  by  their  final  union.  The 
canal  is  the  foundation  of  the  entire  adult  nervous  system.  Beneath 
and  parallel  with  the  canal  is  found  the  notochord,  the  forerunner  of 
the  spinal  column.  The  brain  and  spinal  cord  are  gradually  evolved 
from  the  medullary  canal  by  reason  of  the  specialization  of  some  of 
the  cells  constituting  the  walls  of  the  canal. 

The  mesoderm  takes  its  origin  from  a  double  source;  most  of 
its  cells  come  from  the  entoderm,  but  yet  some  are  derived  from  the 
ectoderm. 


REPRODUCTION.  553 

After  its  formation  the  mesoderm  grows  by  reason  of  its  own 
cell-proliferation,  and  is  independent  of  its  dual  source.  Along  either 
side  of  the  median  line  the  mesoderm  presents  a  thickening  of  cells 
(vertebral  plate),  which  becomes  laminated  laterally  (lateral  plate). 
From  the  vertebral  plate  develop  the  somites;  the  lateral  plate  splits 
into  two  lamella?,  of  which  the  outer  is  the  somatic  mesoderm;  the 
inner,  the  splanchnic  mesoderm. 

The  former  unites  with  the  ectoderm  to  form  the  somatopleure, 
while  the  latter  unites  with  the  entoderm  to  form  the  splanclinopleure. 
Between  the  somatopleure  and  the  splanchnopleure  there  is  an  opening, 
the  body-cavity,  from  which  arise  the  serous  cavities  of  the  adult. 

Derivatives  from  the  Layers. 

Epiblast. — From  the  epiblast  are  developed  the  central  nervous 
system  and  the  epidermal  tissues. 

Mesoblast. — From  the  mesoblast  arise  most  of  the  organs  of  the 
body.  These  include  the  vascular,  muscular,  and  skeletal  systems; 
also  the  generative  and  excretory  organs;  but  not  the  bladder,  the 
first  part  of  the  male  urethra,  nor  the  female  urethra. 

Hypoblast.  —  The  hypoblast  is  the  secretory  layer.  From  it 
spring  the  intestinal  epithelium  and  that  of  the  glands  which  open 
into  the  intestines;  also  the  epithelium  of  the  respiratory  system, 
the  bladder,  the  prostatic  part  of  the  male  urethra,  and  the  entire 
female  urethra. 

Up  to  this  point  the  cavity  of  the  germ  is  one  undivided  compart- 
ment bounded  by  splanchnopleure.  By  infolding  of  the  splanchno- 
pleure this  cavity  is  divided  into  two  smaller  compartments  of  unequal 
size.  The  smaller  one  is  the  gut-tract;  the  larger,  the  yelk-sac,  or 
umbilical  vesicle.  The  communication  between  the  two  cavities  is 
the  mtelline  duct. 

With  the  unfolding  of  the  splanchnopleure  the  somatopleure 
also  follows  to  form  the  body-walls  of  the  embryo.  Part  of  the 
somatopleure  becomes  so  lifted  up  as  eventually  to  curl  up  and  over 
the  embryo  until  the  fold  of  one  side  fuses  with  that  of  the  other. 
That  is,  there  is  formed  the  amniotic  membrane  and  cavity.  The 
amnion  is  a  membranous  sac  consisting  of  two  layers  of  embryonal 
cells.  The  inner  layer  is  composed  of  ectodermic  cells,  the  outer 
layer  of  mesodermic  cells.  The  false  amnion,  or  serosa,  comprises 
all  that  part  of  the  somatopleure  which  does  not  go  to  form  the  body- 
Avail  and  the  true  amnion.  It  is  also  called  the  primitive  chorion  and 
by  some  authors  the  chorion.  The  allantois  growing  forth  from  the 


554  PHYSIOLOGY. 

gut-tract  unites  with  its  inner  surface  and  thus  gives  it  vascularity. 
It  is  the  outermost  envelope  of  the  germ.  The  amniotic  sac  is  filled 
with  a  fluid  in  which  floats  the  foetus. 

The  function  of  the  yelk-sac  is  to  furnish  nutrition  to  the  embryo 
for  a  certain  length  of  time,  but  is  very  rudimentary  in  man.  As  the 
yelk-sac  disappears  by  degrees,  its  place  is  taken  by  the  allantois.  The 
latter  then  serves  as  a  medium  of  nutrition  and  respiration  until  the 
formation  of  the  placenta  at  the  end  of  the  third  month. 

Chorion.  —  The  chorion  is  the  membrane  which  envelops  the 
ovum  subsequent  to  the  appearance  of  the  amnion.  It  results  from 
the  fusion  of  the  allantois  and  false  amnion. 

Upon  the  surface  of  the  chorion  are  numerous  villi.  At  first  they 
are  uniform  in  size,  but  at  the  latter  half  of  the  first  month  there  de- 
velops, an  area  the  villi  of  which  are  noted  for  their  long  prolonga- 
tions: the  chorion  frondosum.  This  eventually  becomes  a  portion  of 
the  placenta.  The  remaining  villi  atrophy  and  finally  disappear. 

Placenta. — The  placenta  is  the  nutritive,  excretory,  and  respir- 
atory organ  of  the  foetus  from  the  third  month  to  the  end  of  preg- 
nancy. It  is  discoid  in  shape,  one  side  being  attached  to  the  uterine 
wall,  the  other  becoming  attenuated,  to  end  in  the  umbilical  cord, 
which  is  the  medium  of  exchange  between  the  placenta  and  the 
foetus.  The  villi  of  the  chorion  frondosum  dip  down  into  the  mucous 
membrane  of  the  uterus,  to  push  against  the  walls  of  the  large  vessels 
found  there  and  whose  structure  is  similar  to  that  of  capillaries.  The 
cells  comprising  the  villi  act  as  an  osmotic  membrane  through  which 
osmosis  occurs.  By  this  means  oxygen  and  nutritive  lymph  pass  from 
the  mother's  blood  to  that  of  the  foetus.  On  the  other  hand,  the 
foetal  blood  gives  off  carbon  dioxide  and  probably  urea.  There  is  no 
intermingling  of  the  two  blood-currents,  since  there  is  always  a  layer 
of  epithelium  to  act  as  a  limiting  membrane. 

Foetal  Circulation. — The  blood  is  brought  to  the  body  of  the 
foetus  by  the  umbilical  vein.  Some  of  this  oxygenated  blood  passes 
through  the  liver  to  the  hepatic  veins,  to  be  emptied  into  the  inferior 
vena  cava.  The  remainder  of  the  umbilical  blood  passes  into  the 
inferior  vena  cava  through  the  ductus  venosus. 

The  blood,  mixed  with  that  which  is  returned  from  the  lower 
extremities,  enters  the  right  auricle.  Guided  by  the  Eustachian 
valve,  it  passes  over  into  the  left  auricle  through  the  foramen  ovale. 
The  blood  now  courses  through  the  left  ventricle,  aorta,  the  hypogas- 
tric  and  umbilical  arteries  to  the  placenta. 


REPRODUCTION.  555 

The  blood  is  returned  from  the  head  and  the  upper  extremities 
to  the  right  auricle  by  the  superior  vena  cava.  This  stream  of  blood 
passes  through  the  auricle  and  auriculo-ventricular  opening  directly 
into  the  right  ventricle,  guided  by  the  tubercle  of  Lower.  The  blood 
next  passes  into  the  pulmonary  artery.  Some  of  it  (enough  to  nour- 
ish the  solid  lung-substance)  passes  to  the  lungs,  but  the  major  por- 
tion passes  into  the  aorta  through  the  ductus  arteriosus.  When  in 
the  aorta  it  takes  the  course  of  the  blood  from  the  left  ventricle  to 
finally  reach  the  placenta.  The  blood  to  the  lungs  returns  to  the  left 
auricle  through  the  pulmonary  veins. 

After  birth  the  umbilical  arteries  are  obliterated  with  the  excep- 
tion of  their  lower  portions,  which  remain  as  the  superior  vesical 
arteries.  The  umbilical  vein  becomes  obliterated  and  remains  as  the 
round  ligament  of  the  liver.  The  umbilicals  become  impervious  soon 
after  cessation  of  the  placental  circulation. 

The  foramen  ovale  closes,  thereby  cutting  off  communication 
between  the  right  and  left  hearts.  By  the  second  or  third  day  the 
ductus  arteriosus  has  also  become  obliterated,  to  be  present  in  adult 
life  as  the  ligamentum  arteriosum. 

These  changes  in  the  circulatory  apparatus  are  dependent  upon 
the  establishment  of  pulmonary  respiration  at  birth.  The  first  in- 
spiration is  said  to  be  due  to  a  sensory  reflex  from  the  colder  air 
striking  the  sensory  skin  filaments  of  the  chest  and  abdomen.  After 
the  cord  is  tied  there  soon  follows  an  increase  of  C02  in  the  blood. 
By  its  presence  the  activities  of  the  respiratory  center  of  the  medulla 
are  instigated.  However,  the  various  centers  are  but  feebly  irritable 
at  birth  and  require  somewhat  heroic  stimulation  to  bring  out  their 
activities.  This  feebleness  accounts  for  the  remarkable  vitality  of 
the  infant  and  its  intense  resistance  to  asphyxiation. 

LiTEEATURE  CONSULTED. 

Heisler's  "  Embryology." 


INDEX. 


ABSORPTION,  102,  103 

by  skin  and  lungs,  122 

in  large  intestine,  104 

in  small  intestine,  103 

in  stomach,  102 

of  carbohydrates,  106 

of  proteids,  106 

of  salts,  106 

of  water,  106 

rapidity  of,  114 
Acetic  fermentation,  100 
Achromatic  nuclear  substance,  12 
Action  of  brain  extract,  474 
Adipocere,  373 
Adrenalin,  93 
Afferent  impulses,  466,  467 
Air,  273 

complemental,  255 

-passages,  241 

quantity  of,  breathed,  253 

reserved,   255 

residual,  255 

tidal,  254 
Albuminates,   32 
Albuminoids,  34 
Albumins,  32 
Alcohol,  40 

Alcoholic  fermentation,  100 
Alimentary  canal,  43 

substances,  24,  34 
Amoeba,  14 

movements  of,  15 
Amylopsin,  80 
Amyloses,   27 
Animal  heat,  338,  339 
estimation  of,  344 
extremes  of  temperature,  343 
postmortem  temperature,  rise  of,  357 
Animals,  341 

cold-blooded,   341 

temperature  of,  341 

warm-blooded,  341 
Anosmia,  495 
Anterior  pyramids,  422 
Antipyrin,  356 
Aphonia,  392 
Apnnfia,   261 

Aqueduct  of  Sylvius,  433 
Aqueous  humor,  515 
Arcuate  fibers,  427 
Arginin,   83 
Arterial  blood,   127 
Arteries,  196 

elasticity  of,  203 

rate  of  movement  of  blood  in,  222 

structure  of,  197 

Artery  of  cerebral  haemorrhage,  443 
Artificial  respiration,  264 
Asphyxia,  261 

effect  on  circulation,  263 
Auditory  nerve,  504 
Auditory  striae,  423 
Auricles  of  heart,  171 
Avogadro-Van't  Hoff  law,  111 

BACTERIAL,  digestion,  99 


Beckman's  differential  thermometer,  111 

Beef-tea,   35 

Beer,  40 

Bell's  palsy,   541 

Betatetrahydronaphthylamin,  349 

Bile,   88 

•    acids  of,  89 

action  of  drugs  on,  97  , 

cholesterin,  91 

composition  of,   88 

mucin,  88 

pigments,   90 

salts,  88 

test  for,  Gmelin's,  90 
Hay's,  89 
Pettenkofer's,  90 

uses  of,  92 
Biology,  2 
Bladder,  326,  299 
Blood,  124,  142 

arterial,  127 

cause  of  movement,  212 

color  of,  125 

composition  of,  127 

plates  of,  138 

quantity  of,  126 

reaction   of,   125 

specific  gravity  of,  125 

temperature  of,  344 
estimation  of,  344 

venous,  127 
Blood-corpuscles,  128 

chemistry  of,  141,  142 

count  of,  131,  132 

destruction  of,  141 

experiment  upon,  133 

formation  of  red,  139 

life-cycle  of,   130 

parasites  of,  129 
Blood-gases,  271 
Blood-pressure,  212,  213 

effect  of  vagus  on,  220 

extremes  of,  219 

in  man,  218 

measurement  of,  216,  217 

respiratory  wave.  220 
cause  of,  220 

Traube-Hering  curve  of,  220 

variations  of,  213,  214 
Boyle- Van't  Hoff  law,  111 
Brain,  435 

aqueduct  of  Sylvius,  433 

artery  of  haemorrhage,  443 

blood-supply  of,  442 

claustrum,  439 

corpora  quadrigemina,   440 

corpora  striata,  439 

external   form,   435 

fissures,   435,   436 

ganglia  of,  438,  439 

internal  capsule,  440 

optic  thalamus,  438 

structure  of  convolutions,  436,   437,  438 

tract,  cortico-pontal-cerebellar,  441 
motor,   441 
sensory,  442 


(557) 


INDEX. 


Bread,  40 

Bread-juice,  64 

Bromelin,  63 

Bronchi,  241 

Buffy  coat,  156 

Bulbar  nerves,  459 

Butter,   38 

Buttermilk,  38 

Butyric  fermentation,  100 

CACHEXIA  strumipriva,  287 

Caffeine,  41 

Caisson  paralysis,  275 

Calamus  scriptorius,  423 

Calorie,  345 

Calorimeter,   346,   347 

Capillaries,  199 

Capillary  circulation,  209,  210,  211 

blood-pressure  of,  221 

swiftness  of,  212 
Carbohydrates,   27,  35 
Carbon  monoxide,  145 
Carbonic  acid,   318 
Cardiac  impulse,  175 
Cardiac  pathology,  175 
Cardiac  revolution,  173 
Cardiograms,   177 
Cardiographs,  176 
Caseinogen,  37 
Cell,   1 

achromatic  nuclear  substance,  12 

constituent  of,  10 

definition  of,   7 

fatigue  of,  23 

nuclear  sap,   12 

nucleolus,  12 

nucleus,  12 

vegetable,  6 
Cell-division,   16 

direct,  19 

indirect,  20 
Cement,  48 
Center  of  smell,  495 
Centrosome,  13 
Cereals,  39 
Cerebellum,  461 

afferent  impulses,  466,  467 

corpus  dentatum,  462 

cortex,  structure  of,  464 

efferent  impulses,  467 

function  of,  465 

internal  structure,   462 

nuclei  of,  463 

peduncles,  464 

Purkinje  cells,  464 

section  of,  467 

spinal-cord  connections,   465 

surface  form,  462 
Cerebral  cortex,  437,  470 
ablation  of,  472,  473,  474 
action  of  brain  extract  on,  474 
motor  centers  in,  470,  472 
sensory  centers  of,  470,  472 
Cerebral  peduncles,   431,  468 
crusta,  432 
locus  niger,  432 
tegmentum,  432 
texture  of,  431 

Cheyne-Stokes  respiration,  266 
Chlorides,   318 
Cholesterin,  91 
Chorda  tympani,  541 
Chorion,  554 

Chromatic  aberration,  519 
Chromatic  nuclear  substance,   12 
Chyle,  118 

Ciliary  movement,  15 
Circulation,   163,   164 

course  of,  172 

in  brain,  226 

system  of,  165 


Circulation  of  blood,  199,  200,  201,  202 

duration  of,  224 

rapidity  of,   221 
Claustrum,  439 
Coagulation  of  blood,  153,  154,  155 

condition  affecting,  157 

rapidity  of,  156 
Cocoa,  41 
Coffee,  41 
Coffeon,  41 

Cold-blooded   animals,   341 
Colloids,   111 
Colon  bacillus,  99 
Color-vision,  523,  524 
Colostrum,  38,  291 
Complemental  air,  255 
Complementary  colors,  525 
Compressed  air  of  caisson,  274 
Conjugate  deviation,   536,  537 
Conjugated  sulphates,   97 
Coronary  arteries,   182 
Corpora  quadrigemina,  440,  468 
Corpora  striata,  439 
Corpus  dentatum,  462 
Corpus  striatum,   356,   469 
Cortico-pontal-cerebellar  tract,  441 
Coughing,  266 
Cranial  nerves,  530 
decussations  of,  532 
origin  of,  530,  531 
Creatinin,  315 
Cresol,   99 
Cretinism,  281 
Cruciate  centers,  351 
Crusta,  432 
Cryoscopy,  111 
Crystalline   lens,   515 
Crystalloids,   113 

DALTONISM,  525 
Defecation,  101,  102 
Deglutition,   50,   51 

of  fluids,  52 

of  solids.  51 
Dendrons.  400 
Development,  337 
Diabetes,  95 
Diabetic  puncture,  96 
Diapedesis,  137 
Diet,   336 
Digestion,    42 
Dioptrics,  518 
Diplopia,  534 

Dubois-Reymond  induction  coil,  394 
Dynamometer,  383 

EAR,  496 

Electrolytes,   109 
Electro-physiology,    394 

Dubois-Reymond  induction  coil,  394 

electrical      phenomena     of     contracting 
muscle,    396 

negative  variation  of  nerve-current,  396, 
397 

nerve-muscle  preparation,   394 

physiological  rheoscope,  394 
Electrotonus,   448 
Embryonal   area,   552 
Emulsification,  30 
Enamel,   48 

Endocardiac  pressure,  127 
Enterokinase,  98 
Entoptic  phenomena,   522 
Enzymes,   107 

classification,  107 
Epiblast,   553 
Erepsin,   98 
Eustachian  tube,  505 
Expiration,  250,  252 


INDEX. 


559 


FACIAL  nerve,  540 

Bell's  palsy,  541 

chorda  tympani,   541 

pathology  of,  541 

physiology  of,  541 
Faeces,  100 

amount  of,  100 

color  of,  101 

composition  of,   100,  101 
Fats,  29,  50 
Fauces,  46 
Fechner's  law,  479 
Fecundation,  548 
Fehling's  test,  322 
Ferment,   55 

definition  of,  55 
Fermentation,   99 

acetic,  100 

alcoholic,  100 

butyric,  100 

lactic,   100 

oxalic,  100 

Fermentation  test,  323 
Fertilization,    551 
Fever,   354 
Fibrin,  154 
Fibrin-ferment,  155 
Fillets,   434 
Filtration,  113 
Flesh-juice,  64 
Postal  circulation,  555 
Foods,   330 

caloric  value  of,  337 
Fourth  ventricle,  432,  433 
Fractional  reproduction,  548 
Freezing-point,  112 
Function  of  eye,  518 

GALL-BLADDER,  83 
Ganglia  of  heart,  185 
Gastric  digestion,  57 
Gastric  juice,  60 
action  of,  67,  68 
composition,  61 
flow  of,  64 
secretion  of,  61 

Gay-Lussac-Van't  Hoff  law,  111 
Glands  of  the  intestine,  73 
Globulins,   33 

Glomerules  of  kidney,  340 
Glosso-pharyngeal,  542 

nerve  of  Jacobson,  542 

pathology  of,   542 

physiology  of,  542 
Glucoses,  27 
Glycocholic  acid,  89 
Glycogen,  373 
Gmelin's  test  for  bile,  90 
Growth,    337 
Guaiac  test,  160 
Giinsberg's  test  for  hydrochloric  acid,  75 

H^EMATOCRIT,    132 

Haematoporphyrin,  145 
Haemin,   144 
Haemoglobin,  143 

amount  of,   149 
Haemometer,  150 
Haemorrhage,    157 
Hair,   485 

Hay's  test  for  bile,  89 
Hearing,  496 

anatomy,  496,  497,  498,  499 

auditory   nerve,   504 

binaural   audition,   508 

ear,   496 

Eustachian  tube,  505 

organ  of  Corti,  502,  503,  504 

semicircular  canals,   500,  501 

theory  of  hearing,  507 


Heart,   165 

areas  of  audibility,  181 

auricles,  171 

cause  of  sounds,  179,  180 

effects  of  drugs  on,  195 

frequency,  183,  184 

ganglia  of,  185 

innervation  of,   185 

movements  of,  175 

nerves  of,  189,  190,  192,  193,  194 

nutrition  of,  196 

persistence  of  movements,  178 

position  of  valves,  181 

rhythm  of,  186 

sounds  of,  178,   179 

stimuli  of,  196 

structure  of,  166,  367,  168,  170 

valves  of,  169 

ventricles  of,   171 

work  of,  184 
Heat  unit,  345 
calorie,   345 
calorimeter,  346,  347 
Heller's  nitric-acid  test,  321 
Hibernation,  342 
Hippuric  acid,  314 
Hoarseness,  393 
Hyaloplasm,  9 
Hydrochloric  acid,  69,  70 

test  for  (Gunsberg),  75 
Hypermetropia,  521 
Hyperosmia,  495 
Hypoblast,   553 
Hypoglossal,  546 

physiology  of,  546 

INDICAN,   316 

Indol,  99 

Inspiration,   246,  247,   248,  252 
Intermittent  afflux  apparatus,  203 
Internal  capsule,  440 
Intestinal  digestion,  72 
Intestine,   43,   72 

glands  of,  73 

large,  99 

movements  of,  75 

nerve-supply  of,  76 

structure  of,  74,  75 
Invertin,   99 
Ions,  109 
Iron,  335 
Irradiation,  526 
Isotonic  solution,   133 

JAUNDICE,  97 

KARYOKINESIS,  20 

stages  of,  22 
Kephyr,    38 
Kidney,   299 

blood-vessels  of,   305,  306,  307 

capillaries  of,   308 

glomerules  of,   340 

lymphatics  of,  305 

Malpighian  corpuscles  of,  305 

position  of,   299,   300 

structure  of,   301,  302,   303 

urinary  tubules  of,  304 
Krause's  end-bulbs,  481,  482 
Kumyss,  38 
Kymograph,  217 

LACRYMAL  secretion,  528 
Lacteals,  103,  104,  117 
Lactic  acid,  70,  314 

test  for  (Uffelmann's),  70 
Lactic-acid  bacillus,  37 
Lactic  fermentation,  100 
Lactose,  37 
Large  intestine,  99 
Laryngoscopy,  389 


560 


INDEX. 


Larynx,  385 

condition  of,  390 

muscles  of,  387 

nerves  of,  389 

vocal  cords,  387,  389 
Lateral  columns,  426 
Laughing,  266 
Law  of  Fechner,  479 
Laws  of  sensation,  479 
Lecithin,  91,  406 
Lenses,   522 
Leucin,   83 
Liver,   84 

antitoxic  function  of,  93 

function   of,   87 

gall-bladder,  86 

internal  secretion  of,  94 

structure  of,  84 
Locus  niger,  101,  432 
Lungs,  242 
Lymph,  118 

composition  of,  119 

formation  of,  121 

quantity  of,  121 
Lymphatic  system,  114 
Lymphatic  vessels,   115 

origin  of,  117 

structure  of,  115 

MAMMARY  glands,  291 

effects  on  circulation  of  dried,  292 
Marey's   tympanum,   252 
Mastication,  50 
Matzoon,  38 
Meat,  35 
Meconium,  101 

Medico-legal  tests  for  blood,  161 
Medulla  pblongata,  421 
anterior  pyramids,  422 
arcuate  fibers,  427 
auditory,   423 
bulbar  nerves,  459 
calamus  scriptorius,  423 
centers  in,  459,  460,  461 
external  form  of,  422 
fillets,  434 

fourth  ventricle,  432,  433 
internal  structure  of,  424 
lateral   columns,   426 
olives,  422,  427 
posterior  columns,  426 
restiform  body,  422,  423 
white  columns,  425 
white  substance,  424 
Menstruation,  551 
Mesoblast,  553 
Metabolism,   328,   332,   333 
anabolic  process,  329 
balance  of,  331 
catabolic  process,  329 
effec't  of  starvation  on,  332 
effect  of  work  on,   333 
of  carbohydrates,  334 
of  fats,  333 
of  salts,   334 
of  water,  334 
Methaemoglobin,  145 
Micturition,  327 
Milk,  36,  292 
clotting  of,   37 
colostrum  of,  292 
fats  of,  38 

functional  variations  of,  293 
matzoon,   38 
quantity  secreted,  39 
specific  gravity  of,  37 
theory  of  Ottolenghi,   292 
Milk-juice,  64 
Morphology,  64 
Motor  centers,  471,  472 
Motor  tract,  441 


Mouth,   43,   48 
Mucin,  88 
Muscle-curve,  376 

effect  of  stimuli,  379 

summation  of,   380 

tetanus  curve,  380 
Muscles,   358 

appearance   under   polarized   light,    365 

blood-vessels  of,  366 

cardiac,   367 

chemistry  of,   371 

contractility  of,  369 

elasticity  of,   382 

fibers  of,  360 

influence  of  blood  on,  370 

irritability  of,   369 

nerve-supply  of,  366 

nervous  stimuli  of,  371 
chemical,   371 
electrical,  371 
mechanical,  371 
thermal,  371 

reaction  of,   372 

rigor  mortis,  375 

sound  of,  381 

structure  of,   360,   361,   362,  364 

unstriped,  367 

varieties  of,  359 

work  of,   382 
Myograph,  375 
Myopia,  521 
Myxcedema,  281 

NAILS,  487 
Nerve,  443 

electrotonus,   448 

excitability,  443 

excitability  and  conductivity,  447 

excitants,   447 
chemical,   449 
electrical,    448 
mechanical,  449 

irritability,  444 

of  Jacobson,   542 

Pfliiger's  contraction  laws,  448 

transmission  of  nerve-wave,   445,   446 
Nerve-cell,  398 

dendrons,  400 

neurite,   400 

Nissl  granules  of,  400 

nucleus  of,  400 

structure  of,  399 
Nerve-fibers,    401 

medullated,  402 

myelin  of,  402 

neurilemma  of,  402 

nodes  of  Ranvier,  403 

nonmedullated,   402 

terminations  of,  403 
Nerve-muscle  preparation,  394 
Nerves  of  deglutition,  53 

of  heart,  189,  190,  192,  193,  194 

of  intestine,  76 

of  larynx,  385 

of  respiration,   245,  257 

of  salivary  glands,   56 

of  sweat-glands,  293 

of  taste,  489 

of  tongue,  46 

of  vasomotor  system,  228 
Nervous  system,  398 

anatomy  of,   398 

chemistry  of,  405 

lecithin,  406 

metabolism  of,   407 

neuroglia,  404 
Neurites,   400 
Nodes  of  Ranvier,  403 
Nuclear  sap,  12 
Nuclei  of  cerebellum,  463 
Nucleolus,    12 


INDEX. 


561 


Nucleus,  12 

OBESITY,  337 
Oculomotor,  532 

diplopia,   534 

effect  of  drugs  on,  535 

function  of,   533 

pathology  of,  534 
CEsophagus,  43,  50 
Olein,  30 

Olfactory  organ,  493 
Olfactory  sensation,  493 
Olives,  422,  427 
Ophthalmoscope,   528 
Optic  nerve,  516 

thalamus,  438,  469 
Organ  of  Corti,  502,  503,  504 

of  taste,   489,   490 

of  voice,  385     » 
Osmosis,  109 
Osmotic  pressure,  110 
Ovum,  549 

maturation  of,  551 
Oxalic   acid,   314 

fermentation,  100 
Oxybutyric  acid,  97 
Oxyntic  glands,  62 

PALATE,  45 
Palmitin,  29 
Pancreas,  76 
removal  of,  82 
secretion  of,  77,  78 
secretory  nerves  of,  79 
structure  of,  76 
Pancreatic  juice,   79 

composition  of,  79 

ferments  of,  80 

quantity  of,  80 

reaction  of,  78 

specific  gravity  of,  78 
Papain,  63 

Papilla  of  tongue,  46 
Path  of  motion,  455 
Path  of  sensation,  456 
Pathetic  nerve,  535 
function  of,   535 
pathology  of,  535 
Pawlow's  stomach,  66 
Peduncles,    464 
Pepsin,   63 
Pepsinogen,  62 
Peptone,  33,  69 
Perimeter,  529 
Peristalsis,  75 

pendular  movement,  76 
Pettenkofer's  test  for  bile,  90 
Pfluger's  contraction  laws,  448 
Pharynx,    43,    49 
Phenol,  99 

Phenylhydrazin  test,  322 
Phloridzin,  96 
Phosphenes,   526 
Phosphoric  acid,  318 
Physiological  rheoscope,  394 
Physiology,    2 
Placenta,  554 
Plasma  of  blood,   151 

chemical  properties  of,  151 

gases  of,  153 

inorganic  constituents  of,  151 

organic  constituents  of,  152 

physical  properties  of,  151 
Plasmon,  38 
Plethora,  160 
Pleura,  245 
Pneumogastric,  543 
branches  of,  543 
pathology  of,  544,  545 
physiology  of,  544 


Pons  Varolii,  428,  467,  468 

structure  of,   429 
Posterior  columns,  426 
Prehension,  44 
Presbyopia,  521 
Proteid  compounds,  32 
Proteids,  30,   35 

classification  of,  31 
Proteoses,   68 
Protoplasm,   8 

constituents  of,  10 

movements  of,  14 

specific  gravity  of,  10 
Proximate  principles,  26 
Pulmonary  artery,  pressure,  276 

action  of  drugs  on,  276 
Pulse,  205,  206,  208 

dicrotic,208 
Purkinje  cells,  464 
Pylorus,  59 

QUOTIENT  of  gases,  respiratory,  273 

RAREFIED  air,  275 
Reflex  action,  450 

forms  of,  452 

laws  of,   451,  452 

swiftness  of,  451 
Rennin,  63,  80 
Reproduction,  547 

among  higher  animals,  547 

among  lower  animals,  547 

chorion,  554 

embryonal  area,  552 

epiblast,  553 

fecundation,  548 

fertilization,  551 

foetal  circulation,  555 

fractional  reproduction,  548 

hypoblast,  553 

menstruation,  551 

mesoblast,   553 

ovum,  549 
maturation  of,  551 

placenta,  554 

segmentation,  551 

spermatozoon,   548 
structure  of,   549 
Reserved  air,  255 
Residual  air,  255 
Respiration,  237,  238,  239 

air-passages,  241 

alveoli,  244 

apparatus,  240 

artificial,   264 

bronchi,   243 

carbon  monoxide,  274 

center  of,  258 

chemistry  of,  267 

Cheyne-Stokes  respiration,   266 

compressed  air,  274 

expiration,  250,  252 

function       of       unstriped       muscle 
bronchi,  257 

inspiration,  246,  247,  248,  252 

lungs,  242 

lymphatics,  245 

mechanism  of,  245 

nasal,  257 

nerves  of,  245,  257 

number  of,   255 

pressure,  255 

quotient  of  gases,  273 

rarefied  air,  275 

trachea,  241 

Restiform   body,   422,   423 
Retina,  512,  513,  514,  515 
Retinal  epithelium,  516 
Rhodopsin,   523 
Rigor  mortis,  375 


of 


562 


INDEX. 


SACCHAROSES,  27 
Saliva,  54 

ferment  of,  54,  55 

reaction  of,  55 

reflex  centers,  57 

specific  gravity  of,  55 
Salivary  glands,  48 

action  of  drugs  on,  56 
structure  of,   49 
Salts,  27 

Saponification,  30 
Schuetz's  law,  60 
Sebaceous  glands,  485 

function  of,  485 
Secretin,    78 
Secretion,  277 

adrenal,  285,  286 

internal,  279 

mammary,   289,   290 

pituitary,  288 

spleen,  283 

thymus,  287,  288 

thyroid,  279,  280 
Segmentation,  551 
Semicircular  canals,  500,   501 
Sensation  of  color,  524 
Sensory  centers,  471,  472 
Sensory  tract,  442 
Sighing,  265 
Skatol,   98 
Skin,   480 

action  of  liquids  on,   483 
of  solids  on,  483 

cold  spots,  483,  484 

hot  spots,  483,  484 

Krause's  end-bulbs,  481,  482 

layers  of,  480 

touch-corpuscles,   481 
Skin  radiation  of  heat,  353 
Skin-reflexes,   457 
Smell,  492 

anosmia,  495 

center  of  smell,  495 

hyperosmia,   495 

olfactory  organ,  493 
sensation,  493 

uses  of,   495 
Snoring,   266 
Sobbing,  266 
Somatose,  69 
Sound,  "390 

height  of,   390 

intensity  of,  391 

resonance  of,  391 

timbre,   391 
Sounds  of  heart,  181 

variation  in,   182 
Special  senses,  477 
Spectra  of   blood,    148 
Spectroscope,  147 
Speech,  391 

aphonia,   392 

hoarseness,    393 

stammering,  392 

stuttering,   392 

ventriloquy,    391 
Spermatozoon,   548 

structure  of,  549 
Spherical  aberration,  519 
Sphygmograph,  207 
Spinal  accessory,  545,  546 
Spinal  cord,  407,  420,  449 
anterior   roots,    453 
blood-supply,  effect  of,  452 
centers  in,   457,   458 
central  canal,   415 
columns  of,  416 
commissures,  420,  449,  450 
coverings  of,  408 
diameter  of,    409 
ependyma  of,  415 


Spinal  cord,  exterior  form  of,  409 
fibers  of,  412,   413 
gray  matter  of,  413 
internal  conformation  of,  401,  411 
minute  structure  of,   412 
neuroglia  of,   413 
path  of  motion,  455 

of  sensation,  456 
posterior  roots,   453 
recurrent  sensibility,  454 
reflex  action,   450 
forms  of,  452 
laws  of,  451,  452 
swiftness  of,   451 
skin-reflex,    457 
systemization  of,  415 
tendon-reflexes,  457 
tract,  comma,  419 
tracts  of  anterior  column,  416 
of  lateral  column,  417 
of  Lissauer,  419 
posterior  columns,  418 
trophic  centers,  455 
Spirits,   40 
Spongioplasm,  9 
Stammering,  392 
Stannius's  experiment,  188 
Steapsin,  80 
Stearin,   29 
Stethograph,  251 
Stomach,   43,  57 
action  of  agents  on,   65 
of  alcohol  on,  66 
of  bitters  on,  66 
movements  of,  59 
nervous  control  of,   60 
Schuetz's  law,  60 
secretory  nerves  of,  65 
structure  of,  57,  58 
Stuttering,  392 
Sliccus  entericus,  98 

ferments  of,  98 
Sulphuric  acid,  318 
Swallowing  of  fluids,  191 
Sweat,  294 
acidity  of,  294 
composition    of,    296 
effect  of  drugs  on,  296 
function  of.   298 
pathological  findings  in,  298 
suppression  by  cold,  297 
Sweat-glands,    293 
nerves  of,  294 
structure  of,  293,  295 
Sylvian  center,  351 
Sympathetic,  the,  475,  476 


TACTILE  sense,  477,  478 

law  of  Fechner,  479 

laws  of  sensation,  479 
Taste,  488 

center  for,  491 

effects  of  drugs  on,  491 

organs  of,  489,  490 

variety  of  substances  to  be  tasted,  491 
Tea,   41 
Teeth,  46 

milk,   47 

permanent,  47 

structure  of,  48 
Tegmentum,    432 
Teichmann's  crystals,  145,  160 
Tendon-reflexes,   457 
Tetanus  of  muscle,  380 
Tetany,   2»i 

Thermogenic  center,  348 
Thermo-inhibitory   center,    350 
Thermolytic  center,  352 
Thermotaxic  center,   348 
Thoma-Zeiss  apparatus,  131 


INDEX. 


563 


Thrombosis,   155 
Tidal  air,  254 
Tongue,  46,  488 
Touch,  479 

Touch-corpuscles,    481 
Trachea,  241 
Transfusion,    158 
Trifacial,    537,    538 

motor  function  of,  539 

pathology  of,  539 

physiology   of,    538 

reflex   relations,   539 

trophic  function  of,  539 
Trophic  centers,   455 
Trypsin,  80 

Tuber  cinereum,   350,   352 
Tyrosin,  83 
Tyrotoxicon,   3^ 

UFFELMANN'S  test  for  lactic  acid,  70 
Uhienhuth's  test  for  blood,   161 
Urea,  97,   312 

decomposition  of,  311 

formation  of,  311 

quantity   of,    311 
Ureters,   225 
Uric  acid,  97,  312 

murexide  test  for,  314 
Urinary  tubules,   304 
Urine,    308 

acidity  of,  309 

albumin  in,  321 
Heller's  nitric-acid  test,   321 

bile-pigments,   316 

coloring  matters  of,  315,  316 

composition  of,  301 

drug-pigments,   317 

fermentation  of,  319 

inorganic  constituents,  317 

movements  of  urine,  326 

nerves,  influence  of,  on,  325 

quantity   of,   309 

reaction   of,   buj 

sediment  of,  320 
oxalic,  320 
phosphoric,  321 

specific  gravity  of,   309 

sugar  in,  322 
Fehling's  test  for,  322 
fermentation  test  for,  323 
phenylhydrazin  test  for,  322 

temperature  of,  309 

theory  of  secretion  of,   323 

toxicity  of,  324 

tube-casts,   323 
Urobilin,  316 
Urochrome,  316 
Uroerytherin,  316 

VALVES  of  heart,  169 
Vasoconstrictors,  230 
Vasodilators,  231 
Vasomotor  reflex,  235 
system,  227 

centers  of,  233,  234 

functions  of,   288 

nerves  of,  288 
Vegetable   cell,   6 
Vegetable  foods,  39 
Veins,   198 
blood-pressure  in,  221 


Veins,  rate  of  movement  of  blood  in,  223 

valves  of,  198 
Venous  blood,   127 
Venous  circulation,   225 
Ventilation,  275 
Ventricles  of  heart,   171 
Ventriloquy,  391 
Vision,  509 

accommodation,  520 

after-images,  526 

aqueous  humor,  515 

binocular  vision,  527,  528 

chromatic  aberration,  519 

color-vision,   523,  524 

complementary  colors,  525 

crystalline  lens,  515 

Daltonism,  525 

dioptrics,    518 

entoptic  phenomena,  522 

function  of  the  eye,  518 

hypermetropia,  521 

irradiation,  526 

lacrymal  secretion,  528 

lenses,  522 

lymphatics,  516 

movements  of  eyes,  527 

myopia,   521 

ophthalmoscope,    528 

optic  nerve,  516 

perception  of  light,  517 

perimeter,    529 

phosphenes,  526 

presbyopia,  521 

retina,  512,  513,  514,  515 

retinal  epithelium,  516 

rhodopsin,  523 

sensation  of  color,   524 

spherical  aberration,  519 

transmission  of  light,  509 

visual  angle,   519 
apparatus,  510 

structure  of,  510,   511,  512 
purple,  523 
Visual  angle,  519 
Visual  apparatus,  510 

structure  of,  510,  511,  512 
Visual  purple,  523 
Vital  capacity,  255 
Vitellin,  36 
Vocal  cords,  387,  389 
Voice,   384,    390 

organ  of,  385 
Vomiting,  70 

WARM-BLOODED  animals,  341 

Water,  26 

Wheat,  39 

Whey,   37 

White  columns,  425 

White  corpuscles,  134 

amoeboid  movement  of,  136 

diapedesis  of,  137 

function  of,   136 

number  of,  134 

origin  of,.  138 

varieties  of,   135 
substance,   424 
Wine,  40 

YAWN,  265 


29125 


